Chain Rule Questions

If $64$ people can complete a piece of work in $8$ days by working $12$ hours a day, then how many hours a day should $32$ people work to complete the same work in $15$ days?

If $120$ persons can finish a work within $16\text{days}$ by working $6\text{hours}$ a day, then the number of hours per day that $64$ persons should work to finish that same job within $15\text{days}$ is:

A contractor undertakes to make a tunnel in $40$ days and employs $25$ men. After $24$ days, he finds that only one-third of the road is made. How many extra men should he employ so that he is able to complete the work $4$ days earlier?

If $36\text{ bighas}$ of land can be irrigated in $16\text{ days}$ by a well-pump working $15\text{ hours}$ a day, how many days will it take to irrigate $42\text{ bighas}$ of land using the same pump if it works $10\text{ hours}$ a day?