Let Tower is AB and its shadow is represented by AC and AD at different sun's altitude.Let the angle of elevation of sun at the time of larger shadow is θ, as shown in figure.In triangle ABC,tan60∘=xh​h=3​x...(i)In triangle ADB, tanθ=3xh​tanθ=3x3​x​...[from (i)]tanθ=3​1​⇒θ=30∘