17. At what rate percent per annum will a sum of Rs. 3,600 become Rs. 4,500 in 10 years at simple Interest? a) 10% b) 6.75% c) 2.5% d) 5% 16. A sum doubles in 20 years at simple interest. How much is the rate per annum? a) 12% b) 18% c) 5% 1 d) 4%