Write Gauss's theorem for a charge outside a closed surface?

Define Gauss’s theorem in electrostatics.

A capacitor of capacitance C is charged to a potential V and is placed inside a closed surface. The electric flux through the closed surface is

Show that total electric flux over a closed surface due to charge outside the surface is zero?

If the number of electric lines of force emerging out of a closed surface are 10^3 , calculate the charge enclosed by the surface.

If the flux through a closed surface is zero, then