Determine the exact equation given the following descriptions.

a) Cubic function shifted right 4 units up 2 and through the point (2,18)

b) A square root family shifted left 2 and down 1 through the point (7,9)

c) A circle with a center of (-2, 7) and a radius of 12.

d) A circle with a center of (1, -4) and a radius of 3.