Two identical balls having a mass m and small radii and having equal charge q are suspendended from common point by two insulating strings of equal length l . In equilibrium each string makes an angle $\;\theta\;$ with the vertical . If $\;\theta=45^{0}\;find\;l^2$ in terms of q and m

Question

$(a)\;\large\frac{k\;q^2}{2\;mg}\qquad(b)\;\large\frac{k\;q^2}{4\;mg}\qquad(c)\;\large\frac{k\;q^2}{mg}\qquad(d)\;None$