potential difference problem

[jordanl122]

Two parallel plates having charges of equal magnitude but opposite sign are separated by .12 m. Each plate has a surface charge density of 36 nC/m^2. Determine the potential difference between the plates.

I have to admit I am at a bit of a loss on how to answer this
(lettings S represent the integral sign)
I know Delta V = -SEds
and that E is constant so
Delta V = -ESds so delat V = -Ed
but I am not sure how to find E, I know sigma =Q/A
and I dont see how Gauss' law could really work here

any light someone can shed would be greatly appreciated.

[vsage]

Pretty classic problem. Assume the plate is infinite and make a cylindrical gaussian surface whose length is perpendicular to the face of a sheet: Illustrated in better detail here

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesht.html#c2 Just remember that through the top and bottom of the cylinder flux equal to EA comes out, so the total flux is 2EA.