Alex found an old credit card statement that was sent to him before the enactment of the Credit CARD Act. He had no previous balance but charged $4,000 that month. His credit card account has a monthly percentage rate of 1.5%. He made no additional purchases during that billing cycle. A minimum of $20 was required as a monthly payment. How long would it have taken Alex to pay down his debt if he continued to only pay the minimum amount without making any other credit card purchases?