P and Q completed a work together and were paid ₹1,080 and ₹1,440, respectively. If P can do the entire work alone in 20 days, how many days did they take to complete the work together?

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?