A balloon is moving up in air vertically above a point A on the ground . When it is  at high  h1 ,a girl standing at a distance d (  point B from A)  (see figure) sees it at an angle 450 with respect to the vertical . When the balloon climbs up a further  height  h2, it is seen at an angle 600  with respect to the vertical if the girl moves further by a distance 2.464d   (Point C) . Then the height h2  is ( Given  tan 300=0.5774):