A work was completed by Adhi alone working for 4 days in the beginning, followed by Bala alone working for 3 days. In how many days can Adhi alone do the entire work, if the ratio of Adhi's efficiency to Bala's efficiency is 3 : 1?

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?