16. According to the choice made between the 2 possibilities provided for in section 12, the community shall prescribe that the proportion established under section 13 is to be used to multiply
(1) the proportion established under section 14; or
(2) the sum obtained by adding the parts, determined in accordance with the second paragraph, of the proportions established under sections 14 and 15.
In the case referred to in subparagraph 2 of the first paragraph, the community shall fix two percentages the sum of which is 100% and which, applied respectively to both the proportions referred to in that subparagraph, determine the part of each proportion that is to be considered for the purposes of the addition under that subparagraph.