Compute the scalar suface integral z z k z ds where k is the part of the sphere of radius 3 centered at the origin, that lies in the first octant. (hint: use the parametrization g(θ, φ) = h3 sin φ cos θ, 3 sin φ sin θ, 3 cos φi with domain of definition [0, π/2] × [0, π/2])