Rate of interest
(1) The rate of simple interest payable under Section 36 shall be two per cent per month:
(a) From the date the tax had become payable to the date of its payment or to the date of any assessment under this Act, whichever is earlier; and
(b) From the date on which any amount payable under this Act was due.
(2) For the purpose of this Section interest in respect of parts of a month shall be computed proportionately and month shall mean any period of thirty days.