How do I find the centre of gravity of this object?

[ipocoyo]

Homework Statement

Hi everyone, I need help finding the centre of gravity for this object in order to find its stability in water. However, I am having trouble finding out the centre of gravity.

Homework Equations

N/A

The Attempt at a Solution

[/B]
The answer says that it is 1, but shouldn't it be 1.5? 3/2 = 1.5

 

[Delta2]

We need to know the height of the barges and the height of the platform, however the statement says that the center of gravity is 0.5 above the surface of water, that is d+0.5=1.5m from the bottom of the object.