Chelsea made monthly payments for four years before her $13,440 loan was paid off. The loan had an interest rate of 5.86%, compounded monthly. Chelsea paid $156.60 in service charges. To the nearest tenth, what percentage of the total cost of the loan did her finance charges comprise? Round all dollar values to the nearest cent. a. 13.6% b. 10.9% c. 9.4% d. 11.9%