Francis has a credit card that uses the previous balance method. the opening balance of one of his 30- day billing cycles was 0, but this was his balance for only the first 15 days of the billing cycle

The credit card charges 13% APR. This comes to 1.08% per month, or .01083333 per month. . Assuming that Joey failed to pay the $7,200 by the due date, then he would owe ($7,200 * 1.08%) ÷ 2, since he owed the money for 15 days. When I multiply this I get $38.99999. D. comes closest to this answer at $38.47. I'm not sure why there is a 53 cent discrepancy between my answer and D.  

A person has to pay his credit card debt by the due date, which is normally 20 to 25 days after the billing cycle ends. The problem does not specify whether Joey paid the $7,200 by the due date. In the absence of that information, I have to assume that he didn't pay it.