Dennis and Gail Schultz are looking over the repayment schedule for their $5,500 loan for lake house remodeling at 15% interest for 42 months with a monthly payment of $168.85. They note that the balance after payment 18 is $3,493.39, after 24 is $2,718.43, and after 30 is $1,883.50. How much would they save by paying off the loan earlv at payment (a) 19, (b) 25, or (c) 31?