Initially the worksheet contains 3C, which tells us we have three cats. The only machine we can use is machine one, since it is the only machine that can accept lone cats. Since it is the only possible move, and can only be used in the forward direction, the only move button enabled is its forward button (labeled 2D 5M). So we click on that button.
Machine Number Machines Operation Shorthand 1 one cat into two dogs and five mice 1C 2D 5M 2 one dog into three cats and three mice 1D 3C 5M 3 one mouse into a cat and a dog 1M 1C 1D