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I've looked over numerous surface integral questions, but I just cannot understand how the projection works.

I'm given A: (x+y^2)i - (2x)j + (2yz)k.

S is the surface of the plane 2x+y+2z=6 in the first octant.

How do we know on which plane the projection will work best and how the limits of integration work. The method I've been taught is: 

∫∫ A.n ds, where n is the unit normal vector perpendicular to the surface, and ds = dxdy/n.k, if the projection is onto the xy plane.

Can someone please solve this question with this method and clear my confusion on limits and where and how to take the projection. 

Thanks a lot!