can this please be explained using the financial calculator Ba-II plus and where to plug in which number

1. Calculating Number of Periods [LO3] One of your customers is delinquent on his accounts payable balance. You've mutually agreed to a repayment schedule of $500 per month. You will charge 1.8 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