(b)the proportion of renewal premium income spent in payment of commission and other expenses in each year during the period since the last investigation after allowing, as the cost of the new business of the year, seven and half per cent of single premiums including consideration for annuities granted and seven and half per cent for each year of the maximum premiums-paying period, but not exceeding ninety per cent in all, of first year's premium falling due in the year after deduction of those unpaid under policies allowed to lapse in the year:
