Use tan= opposite / adjacent .The angle subtended by the tower gives a relation between height and distance.The depression angle from a higher point gives another relation.Solve the two equations to find the horizontal distance. SolutionLet the horizontal distance be d.From ground point:tan30∘=dH⇒H=3dFrom point at height h :tan60∘=dh⇒d=3hThus,d=hcot60∘