A positive charge of magnitude 2 C is at the origin. (a) What is the electric potential

Question:

A positive charge of magnitude 2 μC is at the origin.

(a) What is the electric potential V at a point 4 m from the origin relative to V = 0 at infinity?

(b) How much work must be done by an outside agent to bring a 3-μC charge from infinity to r = 4 m, assuming that the 2-μC charge is held fixed at the origin?

(c) How much work must be done by an outside agent to bring the 2-μC charge from infinity to the origin if the 3-μC charge is first placed at r = 4 m and is then held fixed?