A variable-rate mortgage of $128,000 is amortized over 25 years by equal monthly payments. After 18 months the original interest rate of 6% compounded semi-annually was raised to 6.2% compounded semi-annually. Two years after the mortgage was taken out, it was renewed at the request of the mortgagor at a fixed rate of 6.1% compounded semi-annually for a four-year term. (a) Calculate the mortgage balance after 18 months. (b) Compute the size of the new monthly payment at the 6.2% rate of interest. (c) Determine the mortgage balance at the end of the four-year term