Answer:
5 ft
Explanation:
The shadow of the person is 1/4 the length of the shadow of the building, so the person will be 1/4 the height of the building: 5 ft.
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As this is college math, you would be expected to know that 3 ft × 4 = 12 ft, and 5 ft × 4 = 20 ft. You are also expected to know that shadow lengths are proportional to object heights.