The elevation of an object on a hill is observed from a certain point in the horizontal plane through its base, to be $30^{\circ}$. After walking 120 metres towards it on level ground the elevation is found to be $60^{\circ}$. Then the height of the object (in meters) is :

Question

$$\begin {array} {1 1} (a)\;120 & \quad (b)\;60 \sqrt {3} \\ (c)\;120 \sqrt 3 & \quad (d)\;60 \end {array}$$