Finding charge with mass, length and separation

[Averiex]

I don't even know where to start..

Two styrofoam balls with the same mass (m=9.0x10^-8 kg) and the same positive charge Q are suspended from the same point by insulating threads of length (L=0.98 m). The separation of the balls is (d=0.020 m). What is the charge Q??

 

[betel]

Welcome to the forum.

First you should sketch the situation. Also include all forces acting on the balls.