A 50-foot flagpole is at the entrance of a building that is 300 feet tall. If the length of the flagpole's shadow is 30 feet at a certain time of day, how long is the building's shadow at that time? A. 75 feet B. 150 feet C. 180 feet D. 200 feet

The problem given above makes use of the concept of ratio and proportion. By letting x be the length of the shadow of the building, the proportion becomes,

50 ft / 30 ft = 300 ft / x ft

The value of x from the equation is 180 ft. Thus, the answer is letter C.