delivered the Opinion of the Court.
¶1 Gаnnett Satellite Information Network, Inc. (GANSAT) appeals an order of the First Judicial District, Lewis and Clark County. The District Court upheld the Montana State Tax Appeal Board (STAB)’s May 17, 2007, order that defined “business income” under § 15-31-302(1), MCA. We affirm.
¶2 We review the following issue on appeal:
¶3 Did the District Court properly interpret the definition of “business income” in § 15-31-302(1), MCA, to include both a “transactional test” and an independent “functional test” for determining the existence of business income?
FACTUAL AND PROCEDURAL BACKGROUND
¶4 Gannett owns an affiliated group (Gannett Group) of newspaper publishing and television broadcasting corporations. GANSAT is a first-tier subsidiary of Gannett. GANSAT publishes the Great Falls Tribune and distributes the USA Today within Montana. GANSAT was the only member of the Gannett Group doing business in Montana in 2000. As a result, GANSAT served as the “taxpayer” for corporation license tax purposes and was the only member of the Gannett Group to file a Montana corporation license tax return.
¶5 Gannett acquired Cablevision’s cable television business as part of its acquisition of Multimedia, Inc. (Multimedia), in 1995. Cablevision, a subsidiary of Multimedia, became a second-tier subsidiary of Gannett. Gannett sold Cablevision for over $2.5 billion in 2000. GANSAT deducted the gain recognized from the sale of Cablevision as nonbusiness income on its 2000 Montana corporation license tax return.
¶6 The State of Montana Department of Revenue (DOR) denied GANSAT’s deduction. GANSAT appealed to STAB. GANSAT arpied that DOR improperly had included Cablevision in the same unitary group with Gannett and GANSAT. GANSAT further argued that DOR *335 improperly had denied a nonbusiness income deduction for the gain generated from the Cablevision sale pursuant to § 15-31-302(1), MCA.
¶7 STAB granted partial summary judgment to DOR. STAB announced in an initial ruling that § 15-31-302(1), MCA, clearly states “two sеparate clauses which must be considered in determining whether income is business or nonbusiness income ... a ‘transactional’ and a ‘functional’ test for business income.” STAB did not determine whether GANSAT actually owed corporate tax on the sale of Cablevision. STAB separately determined that Gannett, GANSAT, and Cablevision comprised the same unitary group for the purpose of determining corporate tax owing in Montana.
¶8 GANSAT and DOR filed a joint interlocutory appeal with the District Court pursuant to § 15-2-305, MCA. The parties requested the District Court to rule on STAB’s construction of § 15-31-302(1), MCA, as containing two separate tests for business income, due to the effect of this conclusion of law on the remaining issues before STAB. The District Court granted the petition for an interlocutory appeal. The District Court affirmed STAB’s interpretation of § 15-31-302(1), MCA, as containing a transactional test and a functional test for determining business income. GANSAT appeals.
STANDARD OF REVIEW
¶9 We review de novo an agency’s conclusions of law to determine if they are correct.
Pesarik v. Perjessy,
DISCUSSION
¶ 10 Did the District Court properly intеrpret the definition of “business income” in § 15-31-302(1), MCA, to include both a “transactional test” and an independent “functional test” for determining the existence of business income?
¶11 The “unitary business principle” permits a state to tax a corporation on an apportionable share of the multistate business carried on in the taxing state.
Allied Signal, Inc., v. Director, Div. of Taxation,
¶12 Montana is also a full-member of the Multistate Tax Commission, the administrative agency for the Multistate Tax Compact (Compact). Section 15-1-601, MCA. The National Conference of Commissioners on Uniform State Laws created the Compact to promote uniformity and compatibility in significant components of state tax systems and to avoid duplicative taxation. Sectiоn 15-1-601, Art. I, MCA;
Polaroid Corp. v. Offerman,
¶13 Montana uses the UDITPA’s definitions to divide all corporate income into two categories-“business income” and “nonbusiness income.”
Compare
UDITPA § 1,
7A
U.L.A. 147;
with
§§ 15-31-302 and 15-1-601, Art. IV, MCA. All business income is “apportioned to this state” through a formula based on the property, sales, and payroll of the taxpayer. Sections 15-31-305 to 312, MCA. Montana allocates nonbusiness income generally to the state in which the taxpayer is domiciled. Section 15-31-304, MCA;
see also Hoescht,
¶14 We turn to the definition of business income as set forth in § 15-31-302(1), MCA. The statute defines “[bjusiness income” as “incomе arising from the transactions and activity in the regular course of the taxpayer’s trade or business and includes income from tangible and intangible property if the acquisition, management, and disposition of the property constitute integral parts of the taxpayer’s regular trade or business operations.” Section 15-31-302(1), MCA. “Nonbusiness income” simply “means all income other than business income.” Section 15-31-302(4), MCA. GANSAT and DOR debate the proper construction of the statutory definition of business income.
¶15 GANSAT and DOR agree that the first clause of § 15-31-302(1), MCA, constitutes the “transactional test.” This first clause provides *337 that business income means “income arising from transactions and activity in the regular course of the taxpayer’s trade or business.” The parties dispute the import of the second clause. The second clause provides that business income “includes income from tangible and intangible property if the acquisition, management, and disposition of the property constitute integral parts of the taxpayer’s regular trade or business operations.”
¶16 GANSAT contends that the District Court’s interpretation of the statute renders the first clause “mere surplusage.” GANSAT instead suggests that the second clause modifies the first clause. GANSAT argues that Montana’s definition of business income consists of a single transactional test. DOR agrees with the District Court that the second clause constitutes a separate “functional test” for determining whether certain income is business income. The Multistate Tax Commission supports DOR’s position that the statutory definition of business income contains a separate functional test.
¶17 A majority оf jurisdictions interpret the UDITPA’s definition of business income to include a separate functional test for business income.
Hoechst,
¶18 By contrast, a minority of jurisdictions interpret the UDITPA’s definition of business income as containing only the transactional test.
Hoechst,
¶19 We construe a statute to ascertain the legislative intent and give effect to the legislative will.
State v. Letasky, 2007
MT 51, ¶ 11,
¶20 We interpret a statute first by looking to its plain language. Language that is clear and unambiguous requires no further interpretation.
Letasky,
¶ 11. We turn to extrinsic aids, however, when we cannot garner the legislature’s intent from the plain mеaning of the words used in the statute.
Matter of Estate of Garland,
¶21 We look to the language of § 15-31-302(1), MCA. “Business income” serves as the subject of the sentence. The statute defines business income with two independent clauses. Each of the clauses contains its own verb and subsеquent definitional language. The definition arguably contains a “compound predicate” that states two independent definitions of business income.
See Hoechst, 22
P.3d at 333 (citing
Kroger,
¶22 This interpretation accords with the different language used in the two separate clauses. The first clause focuses on “transactions and
*339
activity” and their relationship to the taxpayer’s trade or business.
Hoechst,
¶23 DOR and GANSAT dispute whether
Mont. Dept. of Rev. v. Am. Smelting and Refining,
¶24 The Court determined that DOR correctly had apportioned a share of the out-of-state gains to Montana because the income was “derived from sources that are integral parts of its business.’’ASARCO,
¶25 STAB also has applied the equivalent of the “functional test” consistently in determining whether the sale of out-of-state real or personal property used in the business should be taxable to a unitary corporation. STAB determined that DOR correctly had apportioned to *340 Montana gain from the sale of Oregon logging equipment where the taxpayer had not converted the equipment to another business or to a nonbusiness purpose before its sale. Harvey Zoon & Sons Logging Co v. Dept. of Revenue, CT-1994-5. STAB similarly determined that DOR properly had apportioned to Montana gain from the sale of Illinois real estate where the taxpayer had designated the property as income producing property before its sale. Decatur Dev., Inc. v. Dept. of Revenue, CT-1996-3.
¶26 We also reasonably could read the definition of business income, however, to contain only a transactional test. The use of the word “includes” after the conjunction linking the two clauses could suggest that the second clause represents a subset of the first. The use of the word “and” in the phrase “acquisition, management, and disposition of property must be integral parts” might suggest that the second clause merely exemplifies the first clause.
Uniroyal Tire,
¶27 We deem the statutory language to be ambiguous and reasonably susceptible to either interpretation of “business income.”
Letasky,
¶ 11. We cannot agree with the District Court’s conclusion that the language of § 15-31-302(1), MCA, clearly sets forth both a transactional test and a functional test for determining business income. We must look to extrinsic aids therefore to determine the legislature’s intent.
Estate of Garland,
¶28 As noted by the parties, Montana’s limited legislative history regarding adoption of the UDITPA proves generally unhelpful in determining the meaning of business income.
Montana Vending,
¶ 21. Montana’s nearly verbatim adoption of the UDITPA prompted little discussion of individual provisions. We look to the UDITPA’s legislative history and official comments in light of Montana’s adoption of the UDITPA and verbatim adoption of the UDITPA’s definition of business income.
Angel,
¶29 The UDITPA’s legislative history suggests the existence of a separate functional test in the definition of business income. The
*341
California Supreme Court conducted a “carefully reasoned” and “detailed” inquiry into the legislative history, policy, and goals of UDITPA. Walter Hellerstein,
The Business-Nonbusiness Income Distinction and the Case for its Abolition,
92 Tax Notes 1701, 1712 (2001) (describing
Hoechst,
¶30 The UDITPA’s legislative history reveals that the UDITPA definition of “business income” derives from California decisional law. The California courts had employed a separate functional test for business income before development and adoption of the UDITPA by the states.
Hoechst,
¶31 The UDITPA’s official comments further suggest its drafters’ intent to carry forward the independent functional test into the UDITPA.
See Hoechst,
¶32 We also note that no principle demands that income generated by the sale of an asset be treated differently from income that the asset may have generatеd while the taxpayer used the asset in its business. The sale of the asset may constitute an unusual or even extraordinary transaction for the taxpayer. This fact alone fails, however, to justify allocating the proceeds of the transaction to a single state rather than apportioning the income among all of the states in which the taxpayer
*342
operates. Hellerstein,
¶33 Moreover, a business runs the risk of double taxation of business income if the jurisdiction in which it sold the property applied the transactional test while another jurisdiction in which the business operates applied the independent functional test.
See
Hellerstein,
¶34 A similar scenario would result in double taxation if Montana applied the transactional test, as advocated by GANSAT, to a Montana lumber company, operating a unitary business in Montana, California, and Oregon, that sold its Montana timber holdings. Montana would ignore the asset’s role in the unitary business if it determined the sale to be unusual or extraordinary. Montana would allocate the entire gain to Montana. California and Oregon, by contrast, would apportion a share of the gain to their respective states, under the independent functional test applied in those jurisdictions, because the assets proved integral to the taxpayer’s unitary business.
Simpson Timber,
¶35 This scenario highlights the strong policy reasons that support interpreting § 15-31-302(1), MCA, to include both the transactional test and an independent functional test.
See
Hellerstein,
*343
¶36 Courts in several states that have adopted the UDITPA admittedly have found the definition of business income to contain solely a transactional test.
See, e.g., Uniroyal Tire,
¶37 The District Court properly determined that § 15-31-302(1), MCA, contains both a transactional test and a separate functional test for determining the existence of business income. The District Court purported to apply a plain language analysis. We note, however, that the District Court also examined extrinsic evidence of the legislature’s intent. We reach this conclusion based upon our combined review of the language of § 15-31-302(1), MCA, extrinsic aids, such as the UDIPTA’s legislative history, and the UDIPTA’s goals of promoting uniformity among states in the taxation of corporations. We leave it to STAB to determine, in the first instance, whether GANSAT owes any corporate tax on the sale of Cablevision.
¶38 Affirmed.
