[10 points] Gary and Nancy buy a house and take out a $250,000, thirty year mortgage at 4.2% interest, compounded monthly. For the following calculations, either use a formula, showing all your substitu tions in that formula.or use the TVM Solver, showing the values of N, 1%, PV, PMT, FV, P/Y and C/Y. (a) Find Gary and Nancy's monthly payment. 1. ANSWER: (b) After making payments for 20 years, Gary and Nancy decide to pay off the unpaid balance in one lump sum. What is the unpaid balance after 20 years of payments? ANSWER: (c) How much interest did they pay over the 20 years? Show how you calculate this