In the above figure, let AB be the tower and C be the point on the ground 30 m away from the foot of AB from where the point A is observed. Join B, C and A, C. We get a right-angled triangle ABC with right angle at B. BC = 30 m. Also, the angle of elevation of the top of the tower AB from C is 30°. So, ∠ACB = 30°. We need to find the height of the tower, that is, AB.
Hence the correct choice is B.
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