A sum of Rs. 1800 amounts to Rs. 9000 in 4 years at the rate of simple interest. What is the rate of interest? Choose the correct choice from the following answers.
A) 50%	B) 75%	C) 100%	D) 60%	E) 25%
S.I. = (9000 - 1800) = Rs. 7200\   Rate = (100 * 7200) / (1800* 4)= 
<gadget id="calculator">(100 * 7200) / (1800* 4)</gadget>
<output>100</output>
100%   Answer: 100%
<result>C</result>
A sum of Rs. 1800 amounts to Rs. 9000 in 4 years at the rate of simple interest. What is the rate of interest?