Chapter 6.10, Problem 9P

If $F=xi+yj,$ calculate ${\displaystyle \iint F}\cdot nd\sigma$ over the part of the surface $z=4-x^2-y^2$ that is above the $(x,y)$ plane, by applying the divergence theorem to the volume bounded by the surface and the piece that it cuts out of the $(x,y)$ plane. Hint: What is $F\cdot n$ on the $(x,y)$ plane?