Calculate the flow of $\mathbf{F} = (0, 0, y^2 + xz)$ through the hemisphere $x^2 + y^2 + z^2 = 4$, $z \geq 0$, in the direction with a positive $z$-component.
I already calculated the divergence on the hemisphere and got zero. I now need to take away (subtract) the flux thru the disc that closes the hemisphere and as you can see in the question it says "in the direction with a positive z-component." Since it says that I used (0,0,1) as my normal but in the answers they used (0,0,-1). Can someone please explain why they did that?