158.5. The part of the retirement pension to which the spouse is entitled is equal to the amount P obtained by the following formula:
where
“r” is the amount of the retirement pension which, if such a partition were not effected, would be payable for the month following the month in which the application for partition is approved;
“m” is one-half of the number of months in the period of marriage of the spouses;
“c” is the number of months in the combined contributory period of the spouses.