27. Subject to sections 28 and 29, a contributor on authorized leave of absence without pay shall be required, in respect of his absence, to pay an amount calculated as follows:(1) for the first 3 consecutive months of his absence, the amount that he would have been required to pay pursuant to section 36 or 37, whichever applies to him, had he not been absent;
(2) for the remainder of his absence, double the amount that he would have been required to pay pursuant to section 36 or 37, whichever applies to him, had he not been absent.