Simple parrallel plate capacitor problem?

Hi guys,

i'm a little stuck with this problem:

'Two connected conducting plates a distance D apart have a charge q placed at a distance b from one of the plates:
show ratio of charge q induced on the plates is D/D-b and D/b'

This can be modelled as a sheet of charge instead of a point charge.

at a distance D-b from plate A and b from plate B (

E field (e being constant in vacuum) at A then: q/4*pi*e*(D-b)^2
E field at B: q/4*pi*e*b^2

but from here i am stuck!

cheers!