How Do You Solve Basic Electric Field Problems?

[sakrei]

This is a pretty basic problem, but I am a little bit lost. I'm not really sure where to start. Can anyone point me in the right direction? i have all the formulas but its not really helping . The problem is #3 on this link:

http://www.flc.losrios.edu/~landry/Coulomb_Practice.pdf

 

[Päällikkö]

Please, show your own work: https://www.physicsforums.com/showthread.php?t=94379

Start by writing down all the forces acting on the particles.