Agnarr has a credit card with a balance of $20,000 and an APR of 18% compounded monthly. He has been making monthly payments of $400 per month, but he has received a substantial raise and will increase his monthly payments to $480 per month. How many months quicker will he be able to pay off the account? Answers:

a. about 27 months b. about 47 months c. about 34 months d. about 20 months