Compute the flux of the vector field F(x, y, z) = 2xj + yk through the surface S, where S is the part of the surface z = -y + 4 above the square 0 ≤ x ≤ 3, 0 ≤ y ≤ 1, oriented upward.

Again, having trouble finding dA. is it not dA = (0i + j + k)dxdy?