Solve Force on Wheaties Box from Cheerios Box: Mass, Friction, & Force

[mcg5132]

Homework Statement

A box of Cheerios (mass mC = 1.1 kg) and a box of Wheaties (mass mW = 2.9 kg) are accelerated across a horizontal surface by a horizontal force applied to the Cheerios box. The magnitude of the frictional force on the Cheerios box is 2.0 N, and the magnitude of the frictional force on the Wheaties box is 3.5 N. If the magnitude of F is 12 N, what is the magnitude of the force on the Wheaties box from the Cheerios box?

Homework Equations

Fs,max=UsFn
fk=UkFn
F=ma
Fn=mg

The Attempt at a Solution

I'm not entirely sure how to set up this equation, I know F= m1(Ff)-m2(Ff) ... ? Or something along those lines. I'm not sure where to begin really.

 

[kuruman]

Draw a free body diagram of two-box system and put in all the forces that you know are there. Use Newton's Second Law to find the acceleration. Then draw a free body diagram of just the Wheaties box.