Reena took a loan of Tk. 1200 with simple interest for as many years as the rate of interest. If she paid tk. 432 as interest at the end of the loan period, what was the rate of interest?

A 3.6

B 6

C 18

D None of these

Correct Answer: Option C

Let rate = R% and time = R years.

then. (1200 X r X r)/100 =432 12R2