A charge Q is placed at a distance $\;\large\frac{a}{2}\;$ above the centre of a horizontal , square surface of edge a as shown in figure . Find the flux of the electric field through the square surface

Question

$(a)\;\large\frac{Q}{\in_{0}}\qquad(b)\;\large\frac{Q}{3 \in_{0}}\qquad(c)\;\large\frac{Q}{6 \in_{0}}\qquad(d)\;\large\frac{Q}{2 \in_{0}}$