(Annuity payments) Calvin Johnson has a $6,000 debt balance on his Visa card that charges 12.4 percent APR compounded monthly. In 2009, Calvin's minimum monthly payment is 3 percent of his debt balance, which is $180. How many months (round up) will it take Calvin Johnson to pay off his credit card if he pays the current minimum payment of $180 at the end of each month? In 2010, as the result of a federal mandate, the minimum monthly payment on credit cards rose to 4 percent. If Calvin made monthly payments of $240 at the end of each month, how long would it take to pay off his credit card? a. If Calvin made monthly payments of $180 at the end of each month, how long would it take to pay off his credit card? months (Round up to the nearest unit.)