If Rs.64 amounts to Rs.83.20 in 2 years, what will Rs.86 amount to in 4 years at the same rate per cent Simple Interest per annum?

Correct option is D

Given:
Principal = Rs. 64 , Amount = 83.20 , years = 2
Principal(2) = 86, time = 4 years
Formula used:
SI = A - P
SI = (P×R×T)/100
Solution:
83.20 – 64 = (64×R×2)/100
19.2×100 = 64×R×2
R = 1920/128
R = 15%
Simple interest after 4 years at the rate of 15% when principal is Rs. 86
SI = (P×R×T)/100
SI =(86×15×4)/100
SI = 51.6
Amount after 4 years = 86 + 51.6 = Rs. 137.6