FOR Question c immediately before the thirteenth payment, why we need add 9422 ? what is immediately before the thirteenth payment?

FOR Question c immediately before the thirteenth payment,

why we need add 9422 ?

what is "immediately before the thirteenth payment"?

4-21. When you purchased your house, you took out a 30-year annual-payment

mortgage with an interest rate of 9% per year. The annual payment on the mortgage is

$9422. You have just made a payment and have now decided to pay the mortgage off by

repaying the outstanding balance. What is the payoff amount if:

c. You have lived in the house for 13 years (so there are 17 years left on the

mortgage) and you decide to pay off the mortgage immediately before the thirteenth

payment is due?

If you decide to pay off the mortgage immediately before the thirteenth payment, you will have

to pay exactly what you paid in part (a) as well as the thirteenth payment itself:

PV = 80,498.09 + 9,422 = $89,920.09