The angle of elevation of the top of a tower from a point A due north of it is a and from a point B at a distance of 9 units due west of A is Cos-1 (3/√13). If the distance of the point B from the tower is 15 units, then cot α is equal to :
(A) 6/5
(B) 9/5
(C) 4/3
(D) 7/3
