A. The Board of Trustees shall adopt rules for computation of the purchase price for service credit. These rules shall base the purchase price for each year purchased on the actuarial cost of the incremental projected benefits to be purchased. The purchase price shall represent the present value of the incremental projected benefits discounted according to the member's age at the time of purchase. Incremental projected benefits shall be the difference between the projected benefit said member would receive without purchasing the service credit and the projected benefit after purchase of the service credit computed as of the earliest age at which the member would be able to retire. Said computation shall assume an unreduced benefit and be computed using interest and mortality assumptions consistent with the actuarial assumptions adopted by the Board of Trustees for purposes of preparing the annual actuarial evaluation.

B. In the event that the member is unable to pay the purchase price provided for in this section by the due date, the Board of Trustees shall permit the members to amortize the purchase price over a period not to exceed sixty (60) months. Said payments shall be made by payroll deductions unless the Board of Trustees permits an alternate payment source. The amortization shall include interest in an amount not to exceed the actuarially assumed interest rate adopted by the Board of Trustees for investment earnings each year. Any member who ceases to make payment, terminates, retires or dies before completing the payments provided for in this section shall receive prorated service credit for only those payments made, unless the unpaid balance is paid by said member, his or her estate or successor in interest within six (6) months after said member's death, termination of employment or retirement, provided no retirement benefits shall be payable until the unpaid balance is paid, unless said member or beneficiary affirmatively waives the additional six-month period in which to pay the unpaid balance. The Board of Trustees shall promulgate such rules as are necessary to implement the provisions of this subsection.