A sum of money doubles in 3 years at compound interest, compounded annually at the same rate. It will become 4 times itself in _____?

5 years

4 years

6 years

None of these

The sum of money doubles in 3 years, which means it becomes 2 times itself.

Since it's compounded annually at the same rate, the interest rate is consistent.

To become 4 times itself, it needs to double twice more (2 × 2 = 4).

Since it doubles every 3 years, it will double twice more in 2 × 3 = 6 years.

So, the correct answer is: 6 years