When solving anproblem including money a negative answer can represent debt (how much you owe)
The volume is multiplied by 8. For example if you have a 1x1x1 cube the volume is 1. If you have a 2x2x2 cube the volume is 8. If you have a 4x4x4 the volume is 64.
I think you should multiply 5x4=20.
