The rate at which a sum becomes four times of itself in 12 years at simple interest will be:

Amount = 4 times principal

Time = 12 years 

where P = principal, R = rate of interest, T = time

Let the principle be x.

Sum become 4 times in 12 years,

So, S.I = 4x - x = 3x 

​$$\therefore$$ rate of interest = 25%​​​