Answer :

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Let AB be the tower and C, D are two points on the ground. Join B, C, D. Also, join A with C and D. We get two right-angled triangles ABC and ABD with right angle at B. The angles of elevation of the top of the tower from the points D and C are 30° and 60° respectively. So, ADB = 30° and ACB = 30°. We are to find the height of the tower. Also given that the distance from D to C is 20 m. So CD = 20 m.


In ∆ABC,



or,



In ∆ABD,



or,



or,



or,



So, the correct option is (B).

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