Four particles, one at each of the four corners of a square with 2.0-m long edges, are connected by massless rods (Figure 9-45). The masses of the particles are m1= m3 = 3.0 kg and m2 = m4 = 4.0 kg. m4 is farthest from the z axis and m2 is on the z axis. Find the moment of inertia of the system about the z axis.

The moment of inertia of a system of particles with respect to a given axis is the sum of the products of the mass of each particle and the square of its distance from the given axis.
http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html