Answer:
5 more man should be added
Explanation:
Inverse Proportion
The time needed to complete a job is inversely proportional to the number of men working on it.
It means the more men working, the less time needed to complete the job.
We know 20 men can complete the job in 15 days. If the job must be completed in 12 days, then more men are needed, thus the number of men needed is:
25 men are needed which means 25-20 = 5 more men should be added.
5 more man should be added