Finding the force (complicated)?

[papi]

Homework Statement

An object of mass m = 6.70 kg has an acceleration a = (1.17 m/s2)x + (-0.664 m/s2)y. Three forces act on this object: F1, F2, and F3. Given that F1 = (2.71 N)x and F2 = (-1.55 N)x + (2.05 N)y, find F3.
( N)x + ( N)y

Homework Equations

I'll be honest, i have no clue. i know F=ma but have absolutely no clue since there are 3 forces and the x's and y's

 

[aimslin22]

you need to break up all the forces into x and y components. (including mg, normal force) find the net force x and y and use F=ma to find the missing x and y, then add these forces together, (its not just x+y) and that it!

 

[HallsofIvy]

Yes, add the forces but I see no reason to assume that "surface of the Earth gravitation" should be included. The problem says specifically that there are three forces.