An initial investment of Rs. x, when placed in an account offering r% per annum as simple interest over a period of 16 years, grows to five times its original value. If an additional Rs. 240 is added to this principal (making it Rs. x + 240) and then invested at an interest rate of r + 25% per annum compounded annually for two years, the resulting balance is Rs. 6480. Determine the value of 'x'.