[QUE/EM-01003] --- EM-PROBLEM

Two similar balls of mass $m$ are hung from silk threads of length $\ell$ and carry equal charges q.  Assuming $\theta$ to be small show that the separation, $x$, betweeen the balls is given by
$$ x\approx \frac{q^2\ell}{2\pi\epsilon_0 mg} .$$ 
What is the value of $q$ if $\ell=120$cm, $m=10$gm, $x=5$cm ?