Four equal masses m are so small they can be treated as points, and they are equally spaced along a long, stiff wire of neglible mass. The distance between any two adjacent masses is l. What is the rotational inertia I_cm of this system about its center of mass?
1) 1/2 ml^2
2) 3 ml^2
3) ml^2
4) 2 ml^2
5) 4 ml^2
6) 7 ml^2
7) 5 ml^2
8) 6 ml^2