If the discount on Rs. 498 at 5% simple interest is Rs.18, when is the sum due?

Answer: Option D

F = Rs. 498
TD = Rs. 18
PW = F - TD = 498 - 18 = Rs. 480
R = 5%
$$\begin{array}{rl}& TD=\frac{PW\times TR}{100}\\ & \Rightarrow 18=\frac{480\times T\times 5}{100}\\ & \Rightarrow 18=24\times T\\ & \Rightarrow T=\frac{18}{24}=\frac{3}{4}\text{ years}\\ & =\frac{12\times 3}{4}\text{ months}\\ & \text{ = 9 months}\end{array}$$