Homework Help: Finding work from an inclined plane, basic question

A 1.54 kg green toy car accelerates at 1.70 m/s² down a ramp 3.38 m long. If the force of friction acting on the toy car is 1.31 N, how much work is done on the toy car to get it to the bottom of the ramp?

Formulas:
Ep=mgh
W=fd
F=ma
a=gh/d
Fr=u*Fn

I know the acceleration, mass, and distance. Using the formulas Ep=Fd I can do 1.54 * 1.7 * 3.38 which is 8.848 J but it isnt correct. I also tried finding the height of the ramp by using the formula a= gh/d and by getting height i can use the formula Ep= mgh but still 8.84. The right answer is 13.3 J but i dont see how. Help? please as soon as possible thanks guys!

 

Never mind totally forgot about net force!!! Problem solved (: