2. [5 marks] A person is considering taking out a mortgage to buy a home. In this mortgage the bank lends the person an amount of money, SD, but charges an interest rate of r% per month. The person agrees to pay back the loan Via monthly instalments of SM over a payback period of P months. (a) Write down a difference equation for amount of money (in dollars), B" , still owing after n months. Use this difference equation to find a formula for the size of the monthly instalment necessary to pay back the loan in the required P months