It's time to go shopping! You grab your Best Purchase credit card, which has an annual interest rate of 18%. The unpaid balance on your card for the current billing cycle is $285.76. On your shopping trip, you purchase four items: a Blu-ray player, two 4-GB flash drives, and a 19-inch flat-screen television. You purchase all the items with your credit card for a total of $352.18. When the bill comes at the end of the month, you decide to pay the entire total balance.
What is the monthly interest rate on the card? What are the interest charges on the card? (Calculate only on last month's unpaid balance.) What is the total balance on your card?