A contractor employed 60 men to complete a certain work in 50 days. After 20 days, 20 men left the work and he employed 20 women in their place. If each woman works at 35 of the working rate of a man, how many extra days are needed to complete the work beyond the scheduled time?

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?