25. Paying off a Discover card. Assume that you have a balance of $3000 on your Discover credit card and that you make no more charges. Assume that Discover charges 21% APR and that each month you make only the minimum payment of 2% of the balance. a. Find a formula for the remaining balance after t monthly payments. b. On what balance do you begin making payments of $50 or less? c. Find how many months it will take to bring the remaining balance down to the value from part b