To complete the work in 18 days 10 men work 6 hours day
To complete the work in 18 days 1 man work (10 x 6) hours a day
To complete the work in day 1 man will work (6 x 10 x 18) hours in a day (less days, less men, more hours)
To complete the work in 1 day 15 men will work 15(6×10×18) hours a day
∴ To complete the work in 12 days 15 men will work 12×156×10×18 hours a day
(more days, more men, less hours) = 6 hours a day
