Find a formula for a function fx y z whose level surfaces

Question

Question: 1. Find a formula for a function f(x, y, z) whose level surfaces are spheres centered at the point (a, b, c).

2. Find a function f(x, y, z) whose level surface f = 1 is the graph of the function g(x, y) = x + 2y.

3. Find two functions f(x, y) and g(x, y) so that the graphs of both together form the ellipsoid x² + y²/4 + z²/9 = 1.