(20) Credit Card Repayment. Suppose you have a balance of $12,000 on your credit card and the finance charge is 2% per month on the unpaid balance. You decide to make payments of $400 per month until the balance is paid off, without charging any new purchases to the card in the meantime. Develop a mixed model for this situation, and use it to determine how long it will take you to pay off everything you owe. Also note how much the last payment should be so that you reduce the balance to exactly zero. As always, be sure to define your variables and give the difference and functional equations