A 50-foot flagpole is at the entrance of a building that is 300 feet tall. If the length of the flagpoles shadow is 30 feet at a certain time of day, how long is the building's shadow at that time?

The building is 300/50 = 6 times as high as the flagpole, so we expect its shadow to be 6 times as long: 6×30 ft = 180 ft.