(c) Upon establishment of eligibility for a retirement allowance, a member shall be granted an annuity which shall be two percent of the member's average salary multiplied by his or her total service credit, subject to reduction if necessary to comply with the maximum benefit provisions of Section 415 of the Internal Revenue Code and section twenty-eight-a of this article.

In this subsection "average salary" means the average of the highest annual salaries received by the member during any five plan years contained within his or her last fifteen years of total service credit: Provided, That the highest annual salary used in this calculation for certain members employed by the West Virginia Higher Education Policy Commission under its control shall be $4,800, as provided by section fourteen-a of this article.

(d) The disability annuities of all disabled retirants shall be based upon a disability table prepared by a competent actuary approved by the retirement board. Disability annuity benefits will begin the first day of the month following the latter of:

1. (1) Six months of absence caused by said disability;
2. (2) date of written report by physician selected by retirement board stating member is mentally or physically incapacitated for service and that disability is total and likely to be permanent; and (3) termination of employment.