How Far from Origin to Position Third Charge?

[bleedblue1234]

Homework Statement

A charge of 4.0 microcoulombs is positioned at the origin, and a charge of -5.6 microcoulombs is positioned 32.7 centimeters to its right. The charges are not free to move; they are fixed in place. Where on the x-axis must a third charge of arbitrary sign be placed in order to be in electrostatic equilibrium?

Homework Equations

Fc = K(Q1)(Q2)/d^2

The Attempt at a Solution

I tried graphing it and finding the intersection of

4.0/x^2 and -5.6/x^2 + 32.7 but no dice

 

[bleedblue1234]

any tips or anything? this is stumping me...