Amit invested Rs. ‘10x’ in scheme ‘A’ offering simple interest of 25% p.a. and reinvested the interest earned from scheme ‘A’ at the end of 4 years in scheme ‘B’ offering compound interest of 20% p.a. compounded annually. If total amount received from scheme ‘B’ after 2 years is Rs. 8640, then find the value of ‘90x’.