The number of men required to complete a job in a certain amount of time is inversely proportional to the time taken to complete the job. This means that if more men are working, the job will be completed in less time, and vice versa.

In this case, 12 men complete a job in 9 days. If we want the job to be completed in 6 days, we can set up the following proportion:

12 men / 9 days = x men / 6 days

Solving for x gives us:

x = (12 men * 6 days) / 9 days = 18 men

So, 18 men working at the same rate would be required to complete the job in 6 days.