Janice uses her credit card, which carries a monthly APR of 18%, for all of her everyday purchases. She eventually reaches her credit limit of $4,000 and begins to re-evaluate her credit habits. After considering her budget, she determines to dedicate, at most, $80 a month to paying down her credit card balance. If she pays $80 a month without any new charges, how long will it take Janice to pay down her balance?