48 md / 4 men = 12 days. If 3 men are digging 6 trenches in 4 days then that means that they are digging 1.5 trenches per day. This means that each man can dig 0.5 of a trench per day. If you have 4 men digging each day, that means you can complete 2 trenches per day. This means that it will take 12 days to complete 24 trenches, using 4 men.