More electric forces pleaseee help

[BuBbLeS01]

Homework Statement

Charge q2 experiences no net electric force. What is q1? (s=8.71 cm, q=-1 nC.)

Homework Equations

F = K * Q * Q1 / r^2

The Attempt at a Solution

How I solve for Q1 if I don't know F?

 

[BuBbLeS01]

Oh nevermind...I got it!