I'm not sure on C, sorry.
1. 12 sugar cubes
2. 24 sugar cubes
3. 72 by 54 by 144, because it gives you the dimensions for one box so if you need something that will fit 36 boxes then you need to multiply the dimensions by 36.
1. multiply all the dimensions given to find volume
2. you could fit twice as many sugar cubes if they are half the original size so just multiply the 12 by 2
you need to give us more information since we can't answer