Help: Volume of a Hollow Cone

This is my third question on volume of cone already. Yikes. I'm really not getting this.
Here's the image of the problem/solid once again:

http://i55.tinypic.com/2wp096h.jpg

I don't even have a clue for this one. It's hollow, of course. I'm not sure what exactly my book wants me to find. It just says: "Find the volume of each solid."

Apparently, the figure is hollow, but I'm not sure if I'm supposed to find the volume of only the hollow part? or maybe the outside part? I don't understand.

Oh, and some explanation to the answer will be REALLY helpful.
Thanks again!

volume of the solid part = (1/3)pi[5^2 * 7.5 - 4^2 * 6]

Can you finish it?

The fact that the given information includes inside and outside diameters as well as inside and outside heights implies that you will need these data. If simple hollow volume (how much water will it hold) was intendes, the outside height and diameter would not have been supplied.

The volume of a cone is: (1/3)(pi)r^2h

So calculate the volume using the outside data and then the inside data. Subtract the smaller from the larger.

V(outside) = (1/3)(3.1416)(5cm)^2(7.5cm) = 196.35cm^3
V(inside) = (1/3)(3.1416)(4cm)^2(6cm) = 100.53cm^3

V(solid part) = 196.35cm^3 - 100.53cm^3 = 95.82cm^3

It's obviously asking for the volume of the solid part. which is the volume of the outer large cone minus the volume of the small cone, so here it goes : 1/3*pi*(5^2)*7.5 - 1/3*pi*(4^2)*6 = 95.818 or 30.5 pi