Four 2-C point charges are at the corners of a square of side 4 m. Find the

Four 2-μC point charges are at the corners of a square of side 4 m. Find the potential at the center of the square (relative to zero potential at infinity) if

(a) All the charges are positive,

(b) Three of the charges are positive and one is negative, and

(c) Two are positive and two are negative.