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 you need to find the monthly payment of the loan by using the formula of the present value of an annuity ordinary which is
Pv=pmt [(1-(1+r/k)^(-kn))÷(r/k)]
Pv the amount of the loan 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

After that find the total amount paid
366.49×12months×4years
=17,591.52

So Service charge is
18,321.60−17,591.52=730.08

Hope it helps!

The solution to the system of equations (-2,2)