From the top of a tower 100 m. high, the angles of depression of the top and bottom of a pole standing on the same plane as the tower are observed to be 30° and 45° respectively. Find the height of the pole. OR From a point P on the ground, the angles of elevation of the top of a 10 m. tall building and a helicopter, hovering at some height over the top of the building are 30° and 60° respectively. Find the height of the helicopters above the ground.