Determine the net charge contained within the cube

[22steve]

Homework Statement

At each point on the surface of the cube shown in the figure, the electric field is parallel to the z axis. The length of each edge of the cube is 3.7 m. On the top face of the cube = -40 N/C, and on the bottom face of the cube = +10 N/C. Determine the net charge contained within the cube.

Homework Equations

flux = E x A

flux = charge enclosed/ permittivity constant (epsilon-naught)

The Attempt at a Solution

I first plugged the numbers to find the flux of the the ends of the cube, then the plugged that into the second equation to find the charge enclose, but I got a really small number that wasn't right.

 

[rootX]

What number you got?

 

[22steve]

-6x10^13 I meant a really big number.

 

[rootX]

I am getting ..6. ..E-9.

Flux is 684.5 (simply adding two together)
and then electric constant is 8.854E-12

 

[22steve]

Ahh, and then its negative, I didn't add the two together I was only using one. Dumb mistake, but thank you soo much!