The difference of compound interest and simple interest on an amount at the rate of 12% per annum for 2 years is Rs. 90/- then the amount will be -

let the amount be x

at compound interest:
amount = x(1.12)^2 = 1.2544x

at simple interest:
x(.12)(2) = .24x

so ....

(1.2544x - x) - .24x = 90
x(1.2544 - 1 - .24) = 90
x(.0144) = 90
x = 6250