A charge Q $\mathrm{\mu }$C is placed at the centre of a cube. The flux coming out from any one of its faces will be (in SI unit) :

When a charge is at the centre of the cube, total flux coming out of the cube is $\frac{\mathrm{Q}}{{ϵ}_0}$Any cube has 6 identical surfaces so through each surface, $\frac{\mathrm{Q}}{6{\in }_0}$ amount of flux will be coming out. Since Q is in microcoulomb, flux in SI system $\frac{\mathrm{Q}}{6{ϵ}_0}\times {10}^{-6}$