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Answer:
 72.18°
Step-by-step explanation:
The altitude of the front is 28 ft. It cuts the base in half, so the other leg of the right triangle is (18 ft)/2 = 9 ft. You know the tangent relation is ...
 Tan = Opposite/Adjacent
The angle of interest has opposite side 28 ft and adjacent side 9 ft, so we have ...
 tan(elevation angle) = (28 ft)/(9 ft)
 elevation angle = arctan(28/9)
 elevation angle ≈ 72.18°
