Given Principal:$8,000,7%,240daysPartialpayments:On100thday,$3,400On180thday,$2,300 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.)