How do the number of electrons flowing into a light bulb compare to the number of electrons flowing out of it?

A light bulb doesn't have a tiny electron factory inside manufacturing
new ones, and it doesn't have tiny bugs inside that eat electrons. 
Also, the heat and light that come out don't carry electrons.

For every electron that goes into the bulb, exactly one electron
comes out.  The numbers are exactly precisely equal.

Since the pully is a simple machine so the mechanical advantage is a 1