If 9 men working 7.5 hours a day can finish a piece of work in 20 days, then…

If 9 men working 7.5 hours a day can finish a piece of work in 20 days, then how many days will be taken by 12 men, working 6 hours a day to finish the work? It is being given that 2 men of latter type work as much as 3 men of the former type?