Expression for an electric field is given by → E = 4000 x ^ 2 ^ i V...

Electric flux is expressed as $ϕ = \overset{\to}{E} \cdot \overset{\to}{A} = EAcos\theta$, here, $A$ is area of the surface and $\theta$ is the angle between the electric field lines and the normal to $A$.

The flux will be only from DEFG surface as on the surface OABC field is zero and for rest of the surface, area vector is perpendicular to field.

So, $ϕ = EA$

$= 4000 \times ( 0 . 2{)}^{2} \times ( 0 . 2{)}^{2}$

$= 4000 \times 16 \times {10}^{- 4}Vm$

$= 640Vcm$