Problem: Helen recently received a credit card with a nominal interest rate of 21 percent. With the card, she purchased some new clothes for $250. The minimum payment on the card is only $20 per month. If Helen makes the minimum monthly payment and makes no other charges, how long will it be before she pays off the card?
a. 11.4 months
b. 14.2 months
c. 19.9 months
d. 8.0 months
e. The card will never be paid off.