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

We have A planar slab of charge with a charge density ρv=ρvo*sin(2*pi/(2*a)),for -a<x<a

the thickness of the slab 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*D_{x}=Q_{enclosed}

Then I am stuck.

The Q_{enclosed}integration give me some problem.

Please can someone help me to establish the Gauss law to solve the problem?

Thank you