A sum amounts to Rs. 2916 in 2 years and to Rs.3149.28 in 3 years at compound Interest. The sum is ?

P be the principle and R % per annum be rate

P(1 + R/100)³ = 3149.28 – (i)

P(1 + R/100)² = 2916 – (ii)
By dividing (i) and (ii)
(1 + R/100) = 3149.28/2916 R/100 = 233.28/2916
or R =233.28/2916 x 100 = 8 %
P(1 +8/100)² = 2916 or
P × 27/25 × 27/25 = 2916
Or = 1822500/729= Rs.2500