The volume of a sphere with radius r is 4 3 π r 3 . Use that formula to help determine the volumes of the following parts of spheres in problems 45 and 46. 45. All (x, y,z) such that (a) x2 + y 2 + z 2 ≤ 4 and z ≥ 0, (b) x2 + y 2 + z 2 ≤ 4, z ≥ 0, and y ≥ 0, (c) x2 + y 2 + z 2 ≤ 4, z ≥ 0, y ≥ 0, and x ≥ 0.