If the ratio of working efficiency of X and Y is 6 ∶ 5 and that of Y and Z is 5 ∶ 4. If X can complete the work in 4 days, then in how many days the total work will be completed if X and Y are assisted by Z on every alternate day?
1
21/11 days
2
3 days
3
28/15 days
4
2 days