I just need an explanation with the answer on number 22. Thanks

22) On the September 20 billing date, Emilio had a balance due of $597.97 on his credit 22) card. During the next month, Emilio charged an additional $390.98 and makes a payment of $473. The interest rate on the card is 1.1% per month. Using the unpaid balance method, find the finance charge on October 20