Given: A circle with Center C = (-9,3,9) Radius r=5
General eqation for a sphere with center and radius r.
Replace with -9, with 3, with 9 and r with 5.
The intersection of the sphere with the plane z=10 can then be found by replacing z in the equation of the sphere by 10.
Subtract 1 from each side:
Equation intersection with plane z=10: