Solution to: Sneaking Spider
The shortest path between two points in a plane is a straight line. Since the spider moves via the sides of the room only, we can "unfold" the room to make it a plane, as follows:
The shortest path between the spider and the fly is the straight line AC. Since AB has a length of 1.5+3+1.5 = 6 meters and BC has a length of 0.25+7.5+0.25 = 8 meters, AC has a length of 10 meters.