Charge placed between two plates

[yoghurt54]

Homework Statement

A sheet of charge +Q is in between two large plates of a capacitor. The plates are separated by a distance 'S', and are connected to each other by a wire. The sheet of charge is closer to one plate, at a distance 'a' from it.

Show that the ratio to +Q of the charges induced on the plate are

a/S, (S-a)/S

Homework Equations

The Attempt at a Solution

I have no idea how to approach this question. I need to find a way of thinking about how to approach this. I've been stuck on it for weeks.

My only lead on this is that the the wire connecting the two plates should have no current flowing through it, so the electric field between the two plates should be zero.

Is there a net charge induced on the plates? Does the charge on one plate have the same sign as the charge on the other?