Answer
See the detailed answer below.
Work Step by Step
We can assume that the electric field is uniform over the 5 faces of the given shape.
We know that the electric flux through a surface is given by
$$\Phi=\vec E\cdot \vec A=EA\cos\theta$$
At side 1,
$$\Phi_1= EA_1\cos\theta_1$$
where $\theta_1=180^\circ$
$$\Phi_1= (400)(2\times 4)\cos180^\circ=\color{red}{\bf -3.2}\;\rm kN\cdot m^2/C$$
At side 2,
$$\Phi_2= EA_2\cos\theta_2$$
where $\theta_2=\theta_3=90^\circ$
$$\Phi_2= EA_2\cos 90^\circ=\color{red}{\bf 0}\;\rm kN\cdot m^2/C$$
At side 3,
$$\Phi_3= EA_3\cos\theta_3$$
where $\theta_2=\theta_3=90^\circ$
$$\Phi_3= EA_3\cos 90^\circ=\color{red}{\bf 0}\;\rm kN\cdot m^2/C$$
At side 4,
$$\Phi_4= EA_4\cos\theta_1$$
where $\theta_4=60^\circ$
$$\Phi_4= (400)(4\times 4)\cos60^\circ=\color{red}{\bf 3.2}\;\rm kN\cdot m^2/C$$
At side 5,
$$\Phi_5= EA_5\cos\theta_3$$
where $\theta_5 =90^\circ$
$$\Phi_5= EA_5\cos 90^\circ=\color{red}{\bf 0}\;\rm kN\cdot m^2/C$$
