P completes 80% of a certain work in 20 days. Then, with the help of Q, he finishes the remaining work in 3 more days. How many days will Q alone take to finish the complete work?

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?