A sum doubles in 3 years at compound interest; when will it quadruple?

A sum doubles in 3 years at compound interest; when will it quadruple?
A: 4
B: 5
C: 6
D: None of these

For compound interest; if a sum doubles in 3 years; it becomes 2P. To quadruple (4P); use the formula P(1 + r)^t = 4P. Since 2P = P(1 + r)^3; then (1 + r)^3 = 2. For quadrupling