There is 60% increase in an amount in 6 years at simple interest. What will be the compound interest of Rs. 12,000 after 3 years at the same rate

Let P = Rs. 100. Then, S.I. Rs. 60 and T = 6 years.

R= $\frac{100*60}{100*6}$ =10% p.a

Now, P = Rs. 12000. T = 3 years and R = 10% p.a.

C.I= $Rs.12000*1+\frac{10}{100}3-1$
       =Rs.3972