Ratio of work efficiencies of A, B and C is 9 : 10 : 12 and they can finish a particular wok working together is 3 days. What is the ratio of the time required if they worked individually?
1
20 : 18 : 15
2
20 : 15 : 18
3
20 : 18 : 16
4
18 : 16 : 15
5
None of these