(5) Where a part of the licence is transferred in a previous year and sub- section (3) does not apply, the deduction to be allowed under sub- section (1) for expenditure incurred remaining unallowed shall be arrived at by-
(a) subtracting the proceeds of transfer (so far as they consist of capital sums) from the expenditure remaining unallowed; and
(b) dividing the remainder by the number of relevant previous years which have not expired at the beginning of the previous year during which the licence is transferred.