120. Except in the cases in which section 123 applies, where, under a contract or other arrangement, an amount can reasonably be regarded as being in part an amount of capital and in part interest or other amount of an income nature, the following rules apply:(a) the part of the amount that can reasonably be regarded as interest is, irrespective of when the contract or arrangement was made or the form or legal effect thereof, deemed to be interest on a debt obligation held by the person to whom the amount is paid or payable;
(b) the part of the amount that can reasonably be regarded as an amount of an income nature, other than interest, shall, irrespective of when the contract or arrangement was made or the form or legal effect thereof, be included in computing the income of the taxpayer to whom the amount is paid or payable for the taxation year in which the amount is received or has become due, to the extent that it has not otherwise been included in computing the taxpayer’s income.