Amit invests a sum of ₹5400

Let the rate of interest be R% per annum.
Amit's principal: P1 = 5400
Gopal's principal: P2 = 9400
Time: T = 6 years
Difference of SI: SI2 - SI1 = 960
Simple Interest formula:
$ SI = \dfrac{P \times R \times T}{100} $
Difference of SI:
$ \dfrac{P2 \times R \times T}{100} - \dfrac{P1 \times R \times T}{100} = 960 $
$ \dfrac{(P2 - P1) \times R \times 6}{100} = 960 $
$ \dfrac{(9400 - 5400) \times 6 \times R}{100} = 960 $
$ \dfrac{4000 \times 6 \times R}{100} = 960 $
240R = 960
R = $ \dfrac{960}{240} = 4$ %
Answer = 4%