W. Va. Code § 11-24-13c
(b) Components of income subject to tax in this state; application of tax credits and post-apportionment deductions. --
(1) Each taxpayer member is responsible for tax based on its taxable income or loss apportioned or allocated to this state, which shall include:
(c) Determination of taxpayer's share of the business income of a combined group apportionable to this state. --
The taxpayer's share of the business income apportionable to this state of each combined group of which it is a member shall be the product of:
(2) The taxpayer member's apportionment percentage, determined in accordance with this article, including in the property, payroll and sales factor numerators the taxpayer's property, payroll and sales, respectively, associated with the combined group's unitary business in this state and including in the denominator the property, payroll and sales of all members of the combined group, including the taxpayer, which property, payroll and sales are associated with the combined group's unitary business wherever located.
The property, payroll and sales of a partnership shall be included in the determination of the partner's apportionment percentage in proportion to a ratio the numerator of which is the amount of the partner's distributive share of partnership's unitary income included in the income of the combined group in accordance with section thirteen-d of this article and the denominator of which is the amount of the partnership's total unitary income.