Electric field intensity on thin electric sheets

[Cocoleia]

Homework Statement

Homework Equations

The only equations I can think to use would be:

But I'm not sure if they are useful or how they will help.

The Attempt at a Solution

I have the solution, it just isn't detailed...

I don't understand where they get E=1/2ε. Should I be considering these as parallel plate capacitors?

 

[Doc Al]

I don't understand where they get E=1/2ε. Should I be considering these as parallel plate capacitors?

There are three sheets of charge. Each produces a field. To find the field at any point, add up the contributions from each sheet.

What's the field from a sheet of charge? See this: Electric Field: Sheet of Charge