(a) Each participating municipality shall pay to the benefit accumulation fund, as its prior service contribution, an amount equal to a percentage of the compensation of members employed by the municipality for that month.
(b) The rate of contribution is the rate determined annually by the actuary and approved by the board of trustees as being the rate required to fund all obligations charged against the municipality’s account in the benefit accumulation fund within the municipality’s amortization period without resulting in a probable future depletion of that account.