(a) The plane of the square is parallel to the $y-z$ plane. Hence, angle between the unit vector normal to the plane and electric field, $\theta=0^{\circ}$ Flux ( $\Phi)$ through the plane is given by the relation, $\Phi\; = |\vec{E}| A \cos\theta$ $\; = 5 \times 10^{3} \times 0.01 \times \cos 0^{\circ}$ $\; = 50\,\mathrm{N}\,\mathrm{m}^2/\mathrm{C}$ (b) Plane makes an angle of $30^{\circ}$ with the $x$-axis. Hence, angle between the unit vector normal to the plane and electric field, $\theta=60^{\circ}$ Flux, $\Phi\; = |\vec{E}| A \cos\theta$ $\; = 5 \times 10^{3} \times 0.01 \times \cos 60^{\circ}$ $\; = 25\,\mathrm{N}\,\mathrm{m}^2/\mathrm{C}$