Six charges are placed at the certices of a regular hexagon as shown in the figure . The electric field on the line passing through point O and perpendicular to the plane of the figure as a function of distance x from point O is $\;(x > > a)$

Question

$(a)\;zero\qquad(b)\;\large\frac{Qa}{\pi \in_{0}x^3}\qquad(c)\;\large\frac{2Qa}{\pi\in_{0}x^3}\qquad(d)\;\large\frac{\sqrt{3}Qa}{\pi\in_{0}x^3}$