Calculate the flux of the vector field $\vec F = -3\,\mathit{\vec i}+\,\mathit{\vec j}+\,\mathit{\vec k}$ through a cube of side 3 with sides parallel to the axes.
flux =

Suppose that one face of the cube is at $x=0$ and the opposite face is at $x=3$. If the face at $x=0$ is removed, what is the flux through the resulting surface?
flux =