Dana just finished paying off the $15,400 loan she took out four years ago. the loan had 6.68% interest, compounded monthly. if dana paid a total of $18,321.60, how much did she pay in service charges? a. $730.08 b. $366.49 c. $1,028.72 d. $266.76

First we need to calculate the monthly payment using the formula of the present value of an annuity ordinary which is
PV=pmt [(1-(1+r/k)^(-kn))÷(r/k)]
PV present value 15400
PMT monthly payment ?
R interest rate 0.0668
K compounded monthly 12
N time 4years
Solve the formula for PMT
PMT=pv÷ [(1-(1+r/k)^(-kn))÷(r/k)]
PMT=15,400÷((1−(1+0.0668÷12)^(
−12×4))÷(0.0668÷12))
=366.49 monthly payment

Second calculate total payments
366.49×4years×12 months
=17,591.52 paying off the loan+interest

Service charges
18,321.6−17,591.52
=730.08. ..answer

Hope it helps!