A, B and C can do a work separately in 15, 30 and 45 days respectively. They started the work together but B and A left 4 days and 5 days respectively before the completion of the work. In how many days was the work finished ?

12 days

 Let us assume , Extra work done by A and B if they work for 5 days and 4 days more

 A = 6R × 5 = 30R

 B = 3R × 4 = 12R

 Total work = 90R + 30R + 12R = 132R

Total work = Efficiency × Number of days

 Time taken = \(\frac{132}{11}\) = 12 days