FORMULA ONLY PLEASE

Your friend gets a credit card with $20,000 available credit on it and starts charging all their expenses to it - not just groceries, gas, and essentials but shopping sprees, plane tickets and a vacation too. Eventually the card is maxed out. Their statement reads "Minimum Payment due: $35 " so that's the amount they start paying each month to pay off the debt. The credit card company charges 24% interest (annual rate) on the unpaid principal balance. If your friend only pays the minimum payment and doesn't spend any more money using the card going forward, how long in months will it take to pay off the $20,000