A sum of Rs. 18,000 gives a simple interest of Rs. 3,240 in 2 years and 3 months. The rate of interest per annum is:

Correct option is C

Given:
Principle = Rs 18000
Simple interest = Rs 3240
Time = 2 years 3 months = $$2\frac{ 3}{12} = 2 \frac{1}{4} = \frac{9}{4 }$$​yrs
Formula Used:
Simple interest = $$\frac{(P\times R\times T)}{100}$$​​
Solution:
​$$3240= \frac{(18000 \times R \times 9)}{(100 \times 4)} \\\\ \\R=8\% p.a.$$​​