Finding charge on two repelling balls hung from threads

[vaazu]

The text is following:
Two balls are hanged on a stative from the same point with 5 cm threads. If they both had the same charge they would be 6 cm away from each other. Both balls weigh 10 mg. Find the charges.

I think the first step is to find the amount of force needed, but I don´t know how. Then I should be able to find the charges from F=k*q1*q2/r*r. I know it´s easy but could please someone tell me what force I should calculate?

 

[hage567]

What are the forces acting on the balls? Draw a free body diagram.

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[vaazu]

I think the forces are gravitational. The balls interact with each other. F=G*M*m/r*r and both of the balls are lifted by one cm. But how can I find force when there is no time? Force equals mass * acceleration? The interaction between balls might be so small that it´s not relevant.