Place third charge so that it experiences no force

[bosox3790]

1. A +6.2 µC charge is placed at the origin and a -3.9 µC charge is placed at x = 25 cm. At what coordinates can a third charge be placed so that it experiences no net force?



2. F=kq_1q_2/r^2

3. I got 3.48 as the velocity between the first to charges. Now I am stuck.

 

[turdferguson]

Draw out a free body diagram for this third charge. Will its location be inbetween the first 2 charges or to one side? Which one will it need to be closer to?