# Gauss law

Hey, I need help to use the Gauss law in this problem:

We have A planar slab of charge with a charge density ρvvosin(2*pi/(2*a)),for -a<x<a
the thickness of the stab is 2*a.
the horizontal y axis passes through the middle of the stab.
the x axis is vertical
a) Find the electric field vector in the region -a<x<a.

I know I need to use the Gauss law.
But I have some problems to establish the integral.
What surface should I take?

I tried the cylinder as surface of integration.
I got:
FLUX=2(pi)x*L*Dx=Qenclosed
Then I am stuck.
The Qenclosed integration give me some problem.
Please can someone help me to establish the Gauss law to solve the problem?