Answer
The flux through one surface of the cube is $~1.7\times 10^4~V~m$
Work Step by Step
We can use Gauss' law to find the total flux through the cube:
$\Phi = \frac{Q}{\epsilon_0}$
$\Phi = \frac{0.890\times 10^{-6}~C}{8.854\times 10^{-12}~F/m}$
$\Phi = 1.0\times 10^5~V~m$
By symmetry, the flux through each surface is $\frac{1}{6}$ of the total flux through the cube. We can find the flux through one surface:
$\Phi' = \frac{1.0\times 10^5~V~m}{6} = 1.7\times 10^4~V~m$
The flux through one surface of the cube is $~1.7\times 10^4~V~m$
