A charge q is located at the centre of the cube. The electric flux through any face is

According to Gauss's law, $\mathrm{\Phi }=\mathrm{q}/{\mathrm{ϵ}}_0$. There are six faces in a cube. So, the flux coming out through one face will be one-sixth of the total flux. Therefore
${\mathrm{\Phi }}_1=\frac{1}{6}\times \frac{\mathrm{q}}{{\mathrm{\epsilon }}_0}=\frac{\mathrm{q}}{6{\mathrm{\epsilon }}_0}$.