6 men or 5 women can complete a task in 7 days. 6 men work for 5 days and then leave. Find the number of women needed to complete the remaining task in 5 days.

If P and Q together can complete a piece of work in 15 days and P alone can do it in 45 days, in how many days can Q alone complete that work?

A can lay a railway track between two stations in 16 days and B can do the same job in 12 days. With the help of C, they finished the job in 4 days. In how many days can C alone do the job?