Arti and Rita can do a job in 8 hours working together at their respective constant rates, and Arti can do the job alone in 10 hours. In how many hours can Rita do the job alone?

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?