Alright. So we have a rectangular prism 3 long, 2 wide, and 7 high. That would have a volume of 42 because the volume of a rectangular prism is it's length times its width times its height. Now the question is if that prism is made up of cubic centimeter cubes, how many are on the outside? My strategy for this would be to find how many are on the inside. If we were to subtract two from every measurement (getting rid of cubes on the outside, essentially) we would be left with the volume of the cubes that don't touch the outside. Make sense?
3 - 2 = 1
2 - 2 = 0
7 - 2 = 5
So suppose we have a rectangular prism with measurements 1, 0, and 5. The volume is 1*0*5 which is...0. Because the prism is 2 cubes thick, there's nothing that's NOT on the outside. With another similar problem, however, that is how you would solve it.
