Hint: How many batches of rolls can one baker make and bake in 5 hours?

Answer: Five bakers.

2 bakers can make and bake 6 batches of rolls in 3 hours
1 baker  can make and bake 3 batches of rolls in 3 hours
1 baker  can make and bake 1 batch of rolls   in 1 hour
1 baker  can make and bake 5 batches of rolls in 5 hours

So 4 bakers could only make and bake 20 batches of rolls in 5 hours, and we require the extra baker to make and bake the remaining 2 batches of rolls.