The total amount payable in each year by each employer for credit to the employer annuity accumulation fund shall not be less than the sum of the rate per cent known as the normal contribution rate and the accrued liability contribution rate of the total earnable compensation of all members during the preceding year. Subject to the provisions of Section 9-1-1070, the amount of each annual accrued liability contribution shall be at least three per cent greater than the preceding annual accrued liability payment, and the aggregate payment by employers shall be sufficient, when combined with the amount in the fund, to provide the employer annuities and other benefits payable out of the fund during the year then current.