Electric Field Problem

1. Sep 5, 2006

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

2. Sep 5, 2006