A variable-rate mortgage of $141,000 is amortized over 20 years by equal monthly payments. After 18 months the original interest rate of 7% compounded semi-annually was raised to 8.5% compounded semi-annually. Three years after the mortgage was taken out, it was renewed at the request of the mortgagor at a fixed rate of 7.1% 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 8.5% rate of interest. (c) Determine the mortgage balance at the end of the four-year term. (a) The mortgage balance is $ after 18 months. (Round the final answer to the nearest cent as needed. Round all intermediate values to six decimal places as needed.) (b) The size of the new monthly payment is $. (Round the final answer to the nearest cent as needed. Round all intermediate values to six decimal places as needed.) (c) The mortgage balance is $ (Round the final answer to the nearest cent as needed. Round all intermediate values to six decimal places as needed.)