18. The lower window of a house is at a height of 2 m above the ground and its upper window is 4 m vertically above the lower window. At certain instant the angles of elevation of a balloon from these windows are observed to be 60 and 30, respectively. Find the height of the balloon above the ground. Sol. Let B be a balloon at a height GB = x m. 4'm 2'm 1600 (x-6) (x-2) C 4'm 2'm H Let W be the window, which is 2 m above the ground H.