First find the amount of each payment:
\(35,125 = P(\frac{(1+i)^{40} -1}{i (1+i)^{40}}) , i = \frac{.0744}{4} \\ \\ P = 1252.70\)
The total cost will be 40 payments plus service charges.
\(40*1252.70 + 5180.70 = 55,288.90\)
The percentage is the service charge divided by total cost:
\(X = \frac{5180.70}{ 55,288.90} = .0937 = 9.37\%\)