please help me with the question

13. Kristen is planning how to pay for a $1,200 purchase. She has two credit cards. Both cards charge 15% APR interest on the daily average balance if the balance is not paid in full by the end of the billing cycle. The first card has a 10-day billing cycle. The other card has a 30-day billing cycle. Suppose Kristen makes the purchase on the first day of the billing cycle. a. How much will Kristen owe in interest after one billing cycle if she uses the first card? b. How much will she owe in interest after one billing cycle if she uses the second card? c. Suppose Kristen makes payments of $20 every 10 days. What will be the balance on the first card after 90 days? What will be the balance on the second card after 90 days? d. Which card should she use, and why