(d) Using the table, the difference in the monthly payments for each $1,000 is 10.75 - 9.56. So the difference in the monthly payments for each $60,000 is 60(10.75 - 9.56) = d. Over 15 years, you will make 12 x 15 = 180 monthly payments, so the answer is 180d = 180 x 60 x (10.75 - 9.56).