What Is the Center of Mass Position for Three Aligned Cubes?

[Bones]

Homework Statement

Three cubes, of side L1, L2, and L3, are placed next to one another (in contact) with their centers along a straight line as shown in the figure. What is the position, along this line, of the CM of this system? Assume the cubes are made of the same uniform material and L1= 3.5 cm.

http://www.webassign.net/gianpse4/9-44.gif

Homework Equations

The Attempt at a Solution

Xcm=73.5cm^3(d)*1.75cm+294cm^3(d)*7cm+661.5cm^3(d)+15.75cm/73.5(d)+294(d)+661.5(d)
Xcm=12.25
This is not correct and I am not sure what I am doing wrong. I got the area of each cube by multiplying 6*side^2 and then multiplied that by each location of the center of mass and divided by sum of the masses. Please help!

 

[Bones]

Never mind, I figured it out. I was using area and I needed to use volume for a 3D shape.