The Board of Control of the Teachers’ Retirement System shall determine annually the amount to pay the cost of the benefits provided in this article and shall notify the chief fiscal officer of each employer the percentum rate of earnable compensation required to be paid to the retirement system. Each employer of members of the Teachers’ Retirement System of Alabama shall pay on account of the increase provided in this article in the same manner and from the same source of funds as is provided in Section 16-25-21, it being the intent of the Legislature that the cost of providing the increase provided in this article shall be distributed from all funds in proportion to the salaries paid therefrom for active members.