Consider a home buyer planning to purchase a house that is currently worth $400,000. The person will pay $100,000 today as a down payment on the house and borrow from a bank the rest of the purchase price. a) The bank currently offers a 30-year mortgage at the interest rate of 7.2% per year (this is the average mortgage rate as of September 2025). What should be the monthly payment on the mortgage? b) The buyer regrets that the buyer did not purchase a few years ago when the interest rate was low. Sup- pose the mortgage rate is 2.8% per year (this was the average rate as of October 2020) on the 30-year mortgage. Then, what would be the monthly payment on the mortgage