Electric Flux through a square

1. Feb 8, 2010

Cappy9000

The electric field in a certain region of space pints in the z-direction and has magnitude E =5zx, where x and z are measured from some origin. Calculate the flux of that filed through a square perpendicular to the z-axis; the corners of the square are at (x,y,z) = (-1, -1, 1), (-1, 2, 1), (2, 2, 1), and (2, -1, 1). (All fields are measured in N/C, all distances in m).

I used Guass' law Flux = ∯E*dA

After integrating and such I ended up with:

(5zy)|*(.5x^2)| (lower boundary being -1 and upper boundary being 2).

My question is, in the solution z=3; I cannot for the life of me figure out why.