Question 697350
Solution :

Total time taken by all 3 crews to complete work = 10 days
Total work done by all 3 crews in 1 day = 1/10 
Total time taken by crew A alone to complete work = 60 days
Total work done by  crew A in 1 day = 1/60 
therefore, total work done by B and C together in 1 day = 1/10 - 1/60 = 1/12
But B = 3C
B + C = 12
4c = 12
c = 3 days
B = 9 days