What is the electric potential at the center of a square which has sides of length 18 m if
a charge of +1 nC is placed on the top left corner, a charge of +2 nC is placed at the top right
corner, another charge of +2 nC is placed at the bottom left corner, and another charge of +1 nC
is placed at the bottom right corner?
A) 4.2 J/C
B) 3 J/C
C) 9 J/C
D) 9 x 10^9 J/C