Many Lemmings make level work is the third level of the Crazy difficulty, featured in Oh No! More Lemmings.
Strategy
Assign a bomber to the first lemming while he is on the 6th square tile from the left.
Make the second lemming a builder. You can do this anywhere you want (except near the edge), as the only purpose is to delay him.
The first lemming should explode at the very edge of the platform, making a little step that the other lemmings can use to fall safely.
The third lemming should now be the leader of the pack. When he's on the stairs, at the height of the midpoint of the red platform to the right, turn him into a bomber.
The fourth lemming should be assigned a builder, again, just to delay him.
The bomber should explode right at the edge of the red platform, creating a step for the other lemmings to safely fall down and walk to the exit.
Trivia
The title is probably a reference to the saying, "Many hands make light work."