I've attached some slides to help you out with this. I think the best way to approach this question (and the fastest) is trial and error. Try answer choice (A). See if you can put the firefighters behind the gymnasts. When you find a hypothetical where that happens and you've satisfied all the constraints you can rule out answer choice (A) and move on to answer choice (B).
When you try answer choice (B), you shouldn't be able to find any place where you can put the gymnasts followed by the jugglers, such that you satisfy all the constraints. Since you can't make this work, you know that (B) must be the correct answer.
Check out the slides for a visual...
Attachment:
PT43, S4, G1_AtlasLSAT.pdf