An individual who retired before January 1, 2009, and is receiving monthly benefits from the fund on an account paid under this chapter or under former chapter 15-39 on December 1, 2009, is entitled to receive a supplemental payment from the fund. The supplemental payment is equal to an amount determined by taking twenty dollars multiplied by the member’s number of years of service credit plus fifteen dollars multiplied by the number of years since the member’s retirement as of January 1, 2009. The supplemental payment may not exceed the greater of ten percent of the member’s annual annuity or seven hundred fifty dollars. The board shall make the supplemental payment in December 2009.