Ummm... I explained the whole process earlier, and was mistakenly issued for plagiarism. Which really sucks, because it took forever to type and format all of those formulas and steps.
Here's the shortened version...
V=
d (diameter) = 2r
so 24/2 = 12
plug in...
You should get approx. 7234.56, and don't forget to label it appropriately, it should be units cubed.