Net Electric Force Homework: Find Negative Charge Position

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Homework Statement

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In the above figure, if Q1 and Q2 are positive, where could a negative charge be placed and have a vertically upward net force on it?

Homework Equations

F = k|q||q| / (r^2)

The Attempt at a Solution

I wrote the force equations for the negative charge and both positive charges, but I have no idea how to proceed from there.

 

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Please do not reply, I have figured this out