Please explain how to solve using Excel.

Horace has a credit card with a balance of $16,000. The annual interest rate is 15%. The terms of the credit state that a minimum payment of 4% of the outstanding balance must be paid each month, but no less than $40.00 must be paid each month. Horace plans to stop using the credit card and pay off the balance according to the terms of the credit. a. How many years will it take to pay off the balance, assuming Horace only pays the minimum required payment? b. How long will it take to pay off the balance if Horace pays an extra $40.00 per month? c. How much in addition to the required minimum payments must Horace pay each month if he wishes to pay off the balance in 4 years