12. The annual contribution of a municipality to the plan provided for by this Chapter is equal to the sum(1) of the amount corresponding to the proportion represented by the surplus attributed to that municipality over all the surplus established under section 76.1 of the Act, in relation to all the supplementary benefits paid during the year by the Commission under this plan; and
(2) of the amount corresponding to the proportion represented by the surplus attributed to that municipality over all the surplus established under section 76.1 of the Act, in relation to the expenses incurred during the year by the Commission to administer this plan.