Mortgage Calculation and Spreadsheet

Suppose you want to borrow a loan of $400,00 to buy a house.   1. Find your monthly payment.  Then calculate how much you will pay total in 30 years with the rate 3.5% annually.  2.  Suppose that you can an additional amount of $50/month.  Find the number of payments to pay off your mortgage.  Calculate how much you will pay total in this plan.    3. Compare the answer in #1 and #2.  Which plan is  better?   How much time/money do you save? Check this link for other projects on money.