A disk of radius a carries nonuniform surface charge density = 0 (r/a), where

A disk of radius a carries nonuniform surface charge density σ = σ₀(r/a), where σ₀ is a constant.
(a) Find the potential at an arbitrary point x on the disk axis, where x = 0 is the disk center.
(b) Use the result of (a) to find the electric field on the disk axis,
(c) show that the field reduces to an expected form for x >> a.