cannot use excel

how do I solve this? Is there a way to do it without using the log function? Or how could i plug this in to a graphing calculator?

Susaarecantly reseived a credit card with a notminal interest zate of 21 percent. With the card, the putchased some new elothes for $500. The minimum payment oe the eard is only $20 per month. If Susan makes the minimum wonhly payment and makes no other charges, how long wall it be before she pays off the card? selected Answer: b. The eard will tever be pasd off. Answers: a. 232 months 500=1.7520(1(1+1.75) b. The card will never be paid off