Description for Correct answer:
Let the sum be P.

Then, for 4%

SI = (3P-P)=2P

2P = \( \Large \frac{P\times 4\times T}{100} \)=> 1=\( \Large \frac{2T}{100} \)=\( \Large \frac{T}{50} \)

T = 50yr

Again, for another rate (R),

SI =(6P-P) =5P

5P = \( \Large \frac{P\times R\times 50}{100}=\frac{PR}{2} \)

R = 10%