Use stokes' theorem to change ∫∫∇×⋅∫∫s∇×f⋅nds to an equivalent surface integral and evaluate it, where =++=xi+y2j+xyzk, is the upward unit normal, and is the part of the paraboloid z=4−x2−y2z=4−x2−y2 with z≥0z≥0.