Since, Ratan takes 5 days to complete the given work
∴ Ratan finishes 15 part in 1 day.
Similarly, Shankar takes 8 days to complete the work. Therefore, Shankar finishes 18 part in 1 day.
∴ In a day, they together will finish = 15+18=8+540=1340
i.e., 1340 part of the work.
So, they both will take 4013 days 3113 days to complete the work. Hence, the complete work will be finished by them together in 3113 days