You have to place the UP arrow between the red and yellow particles. Then place the RIGHT arrow near the origin of the blue particles. Then place the RIGHT mixer near the green circle in a way that it mixes blue and yellow particles, but dosen't takes all yellow particles. Then place the Left mixer above the blue particle line in a way that it mixes both red and yellow but dosen't mixes blue. If you still have problems I try to upload a image. In the meantime, if someone can give me some help with 3-9, I would appreciate.
well, we could make a walkthrough, but i mean, really. what's the fun in that? some levels are so simple they don't even need that much thinking to complete.