Since you titled this "Stoke's theorem" can we assume you know that theorem? (By the way, it should be "Stokes' " theorem. His name was "Stokes", not "Stoke".)

Stokes theorem says where r is the closed curve bounding surface S.

Since you are asked to find , Stokes' theorem says that you can instead integrate where C is the boundary of that hemi-sphere. When z= 0, so the boundary is the unit circle in the xy-plane. Of course, when z= 0, . I think I might be inclined to integrate around the unit circle by using the angle, , as parameter: , . For the unit circle, .