Electric field

We have an infinite , non conducting sheet of negligible thickness carrying a negative uniform surface charge density sigma, and next to it an infinite parallel slab of thickness D with positive uniform volume charge density p (ro) . All charges are fixed . calculate the direction and magnitude of the electric field .
a) Above the negatively charged sheet.
b)in the slab
c) below the slab
d) make a plot of E as a function of distance z from the sheet.