What is the width of boxes on opposite sides?

• A. 60 ft
• B. 100 ft
• C. 120 ft
• D. 80 ft

Answer: (D)

Think of the width as the distance between two parallel opposite sides. If you’re measuring from a common reference line to each side, those two distances line up on the same perpendicular directions. The gap between the sides sits halfway between those two measurements, so the width is the average of the two distances.

Here the two distances are 60 ft and 100 ft. Halfway between them is (60 + 100) / 2 = 80 ft. That’s why the width comes out to 80 ft. The other numbers would not place the sides at that same constant gap.