Answer: Five bread-men.
2 bread-men can bake 6 rolls in 3 hours,
1 bread-man can bake 3 rolls in 3 hours,
1 bread-man can bake 5 rolls in 5 hours.
So 4 bread-men could only make 20 rolls in 5 hours, and we require the extra bread-man to do the remaining 2 rolls.