79. Subject to the provisions of any law for the time being in force relating to the relief of debtors, and without prejudice to the provisions of section 34 of the Code of Civil Procedure, 1908,(a) when interest at a specified rate is expressly made payable on a promissory note or bill of exchange and no date is fixed from which interest is to be paid, interest shall be calculated at the rate specified, on the amount of the principal money due thereon, from the date of the note, or, in the case of a bill, from the date on which the amount becomes payable, until tender or realisation of such amount, or until the date of the institution of a suit to recover such amount;(b) when a promissory note or bill of exchange is silent as regards interest or does not specify the rate of interest, interest on the amount of the principal money due thereon shall, notwithstanding any collateral agreement relating to interest between any parties to the instrument, be allowed and calculated at the rate of six per centum per annum from the date of the note, or, in the case of a bill, from the date on which the amount becomes payable, until tender or realisation of the amount due thereon, or until the date of the institution of a suit to recover such amount.