To solve this problem, we need to visualize it

To solve this problem, we need to visualize it.For starters, we know that on the correct floor there's one room,let's call it room A,with one door to the control panel room,plus one door to room B,and one to C.So there must be at least four rooms,which we can represent as circles,drawing lines between themfor the doorways.But once we connect rooms B and C,there are no other connections possible,so the fourth floor down from the top is out.