If Vipul invests Rs.’a’ in scheme ‘M’ with a compound interest rate of 20% p.a. for two years, and the total amount received from scheme ‘M’ is reinvested in scheme ‘N’ with a simple interest rate of 15% p.a. for four years, resulting in a total interest of Rs.1296 from scheme ‘N’. What is the total investment amount in scheme ‘N’?