Four point charges q = +3.4 µC are arranged in a square of edge length 1.9 cm.?

Question

Four point charges q = +3.4 µC are arranged in a square of edge length 1.9 cm.
What is the electric potential at the center of the square?

Answer 1

This is a very easy problem. Since the distance from the center of the square to any of the corners is r = (side length)*sqrt(2)/2, and you must have learned the electric potential due to a point charge is: q/(4*pi*eo*r), the requested answer is:
4*q/(4*pi*eo*r)
= 4*3.4x10^(-6)/(4*3.14159*8.854×10^(−12)*0.019*sqrt(2)/2)
= 9.1x10^6 (V)