Four 50-G Point Masses Are at the Corners of a Square

Four 50-g point masses are at the corners of a square with 20-cm sides. What is the moment of inertia of this system about an axis perpendicular to the plane of the square and passing through its center?

A) 1.0  10^-3 kg · m²
B) 4.0  10^-3 kg · m²
C) 2.0  10^-3 kg · m²
D) 8.0  10^-3 kg · m²
E) 2.8  10^-3 kg · m²