Gauss' Law for a Nonuniform Field

[Redfire66]

Homework Statement

A closed rectangular surface with dimensions a = b and c where the faces perpendicular to the field are a*b. The left edge of the closed surface is located at position x = a, for c > a.The electric field throughout the region is nonuniform and given by E = 3*x xhat N/C,

Homework Equations

Flux = Integral of E(dot)dA = qenclosed/Epsilon0

The Attempt at a Solution

I'm just wondering about how this works, if there is no enclosed charge, then there shouldn't be a net flux.

I'm pretty sure the flux at one end is greater as it reaches the x = c face than at x = a, is it possible to have a nonzero net flux?

 

[PietKuip]

Conclusion: there is charge in the box.