Electrostatic force on nonlinear charges

[bigslowy]

http://www.imagebucket.net/images/bigslowy/physicsproblem.jpg
What is the strength of the electrostatic
force on the top charge? Answer in units of N.

I tried breaking it down into components of Fabx + Fbcx ect. but I still don't get a correct answer. Is there a different approach I should take? Any help would be greatly appreciated.

 

[Tide]

You're using the right approach - but you're just not executing it properly.