Hi David,
When you calculate a volume of concrete the usual units are cubic yards, or sometimes people just say yards. The volume of a rectangular slab as you have is given by
volume = length width thickness
Since you want the volume in cubic yards you need to express the dimensions in yards.
there are 3 feet in a yard so
8 ft = ^{8}/_{3} yards
There are 36 inches in a yard so
4 inches = ^{4}/_{36} yards
Thus the volume of your first example is
^{8}/_{3} ^{8}/_{3} ^{4}/_{36} = 0.79 cubic yards
Penny
