The simple interests earned on the sum of money for 4 years at 7.5% p.a. exceeds that on the same sum for 3.5 years at 8% p.a. by $90. (a)Find the original sum of money. (b)If the original sum of money accumulates to $4612.50 in 5 months at simple interest, find the interests rate per annum.

Simple interest = i(n) Using 4 years at 7.5% (0.075), we get: Simple interest = 4(0.075) = 0.3 What is p.a.?