15In estimating the expenditure mentioned in paragraph 13 above which they will incur in respect of any financial year a local authority shall take into account—
(a)such additional sum as is in their opinion required—
(i)to cover expenses previously incurred;
(ii)to meet contingencies; and
(iii)to meet any expenses which may fall to be met before the money to be received from the sources mentioned in paragraph 13 above in respect of the next following financial year will become available; and
(b)any means by which any part of that expenditure may otherwise be met or provided for.