A variable-rate mortgage of $137,000 is amortized over 20 years by equal monthly payments. After 18 months the original interest rate of 6% compounded semi-annually was raised to 7.8% 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 6.2% 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 7.8% rate of interest.

(c) Determine the mortgage balance at the end of the four-year term