Answer
$\Phi = -3.92~N~m^2/C$
Work Step by Step
We can find the electric flux through the right face:
$\Phi = \int E \cdot dA$
$\Phi = (-2.00~N/C)~\hat{j}\cdot (1.40~m)^2\hat{j}$
$\Phi = (-3.92~N~m^2/C)\hat{j}\cdot \hat{j}$
$\Phi = -3.92~N~m^2/C$