Flux integrals - verifying Stokes Theorem

Ok, I've been stuck on this problem for hours now and its really irritating, so I need help!

Here is the question:

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Verify Stokes Theorem for the vector field

F = yi + 2zj + xzk

and the surface S defined by

x^2 + y^2 + z^2 = 25 & Z>=4

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Right, I'm quite new to these so please explain clearly if possible, cheers!

So far I've computed the line integral and got a result of -Pi

Now I'm stuck on the flux integral. I've worked out that Curl F = -2i -zj -k but I'm not sure what the normal vector is or the limits.

Any help much appreciated!