Find the height H of the flagpole

  B  15 ft

Step-by-step explanation:

The length of the left side of the triangle is 6/8 = 3/4 of the length of the base. For shadows in the same general area, the ratio of height to shadow length is the same for all objects. So, we can assume that ...

  h = (3/4)(20 ft) = 15 ft

You can eliminate the other answer choices using your "common sense." The triangles have sides of different measure, and the one corresponding is shorter than the bottom side. Hence 20 and 26.67 make no sense. We also note that the missing side will be more than half the length of the bottom side, so 2.4 makes no sense.