last one help!

Suppose you owe $1.400 on your credit card. The annual percentage rate (APR) is 21%. compounded monthly. The credit card company says your minimum a. If you make only this minimum payment, how long will it take for you to repay the 81.400 balance (assuming no more charges are made)? b. It you make the minimum payment plus $9.74 extra each month (for a total of $37.87), how long will it take to repay the $1 .400 balance? c. Compare the total interest paid in Part (a) with the total interest paid in Part (b) a. It will take months for you to repay the initial balance. (Round to the nearest whole number.)