Answer
a). Amount received at age 65 after 40 year A = 171,271.4
b). Interest = 135,271.4
Work Step by Step
a). Deposit at age 25 per month = 75
Compound interest rate is 6.5% = 0.065
Amount received after n year A = $\frac{P [(1 + \frac{r}{n})^{n\times t} - 1]}{\frac{r}{n}}$
Amount received at age 65 after 40 year A = $\frac{75 [(1 + \frac{0.065}{12})^{12\times 40} - 1]}{\frac{0.065}{12}}$
= $75\frac{ 12.369}{0.00458}$
= 75$\times$ 2283.62= 171271.4
b). Interest = 171271.4 - (75$\times$12$\times$40) = 171271.4 - 36000 = 135271.4
