Given Principal: $8,500, 8%, 240 days Partial payments: On 100th day, $3,600 On 180th day, $2,400 a. Use the U.S. Rule to solve for total interest cost. (Use 360 days a year. Do not round intermediate calculations. Round your answer to the nearest cent.) b. Use the U.S. Rule to solve for principal balances. (Use 360 days a year. Do not round intermediate calculations. Round your answers to the nearest cent.) c. Use the U.S. Rule to solve for final payment. (Use 360 days a year. Do not round intermediate calculations. Round your answer to the nearest cent.)