A flat square with sides of length L is described by the equation $\mathrm{x}=\mathrm{L}, 0<\mathrm{y}<\mathrm{L}, 0<\mathrm{z}<\mathrm{L}$. Find the electric flux through the square due to a positive change q located at the region $(\mathrm{x}=0,\mathrm{y}=0,\mathrm{z}=0)$

Imagine a charge q at the corner of a cube of edge length 2L 

then the flux through the bigger cube will be $\mathrm{\varphi }=\frac{\mathrm{q}}{{\mathrm{ϵ}}_0}$
Here, the square is one 24^th of the surface area of the imaginary cube so it intercepts $\frac{1}{24}$ of the flux 

So, the flux through the square $\mathrm{\varphi }=\frac{\mathrm{q}}{24{\mathrm{ϵ}}_0}.$