A tower standing on a horizontal plane subtends a certain angle at a point 160 m apart from the foot of the tower. On advancing 100 m towards it, the tower is found to subtend an angle twice as before. The height of the tower is
A, B, and C can complete a work in 40, 60, and 80 days respectively. They started working together. If A and B left 11 days and 8 days before the completion of work. In how many days they will complete the work.