5% interest compounded annually for 3 years multiplies the initial balance by
... 1.05^3 = 1.157625
5% simple interest for 3 years multiplies the initial balance by 1 + 3*0.05 = 1.15.
The difference of these multipliers is
... 1.157625 - 1.15 = 0.007625
If the difference in account balance is Rs 61.00, then the invested principal amount P is
... P*0.007625 = 61.00
,.. P = 61.00/0.007625 = 8000.00
The sum of money is Rs 8000.