21. Calculating Number of Periods [LO3] One of your customers is delinquent on his accounts payable balance. Youve mutually agreed to a repayment schedule of $500 per month. You will charge 1.3 percent per month interest on the overdue balance. If the current balance is $18,000, how long will it take for the account to be paid off?

How do you know to use the formula for PVA based on the given information?