Let’s denote the principal amount as P and the rate of interest as R.

Simple Interest (SI) for 6 years:

SI = (P × R × Time) / 100

= (P × R × 6) / 100

Given that the SI is 60% of the principal amount (P):

(P × R × 6) / 100 = 0.6P

Multiply both sides by 100 and divide by 6P:

R = (0.6 × 100) / 6

R = 10

Now, let’s find the compound interest (CI) for Rs. 12,000 after 3 years at 10% per annum:

CI = P × (1 + R/100)^Time – P

= 12000 × (1 + 10/100)^3 – 12000

= 12000 × (1.1)^3 – 12000

= 12000 × 1.331 – 12000

= 15972 – 12000

= 3972

The compound interest is Rs. 3972.