(a) Effective as of October 1, 1974, each female employee shall contribute at the same rates as a male employee for widow’s annuity or other benefits, to the end that like credits may be established and maintained for both male and female employees for all purposes of this Article with respect to annuities, benefits, contribution rates, refunds and other provisions of this Article.
     (b) Any female employee shall have the option of making contributions for the aforesaid purposes covering the period prior to October 1, 1974, and receiving pension credits therefor, including the concurrent credits from city contributions. Such contributions shall include interest at 4% per annum from the dates such contributions should have been made from the beginning of their service to the dates of payment to the end that equal credits may be provided for all employees under this Article.