A certain amount of money becomes 3 times in 12 years. What is the interest rate?

Question: A certain amount of money becomes 3 times in 12 years. What is the interest rate?

Solution:
let the principle amount it X.
so, the Interest = 3X -X = 2X
time, n = 12 years
let,
rate = r%

As we know,
I = Pnr/100
r = (I × 100)/Pn
= (2X × 100)/ 12X
= 16.67%