Okay, so it took me a bit to figure out exactly what it was asking. But once you get that, it's easy.

The key bit of information is that Juanita* doesn't know how many friends she has! She knows that either 4 bags of stickers will work or that 6 bags of stickers will work, but she isn't sure. Assuming without loss that each bag contains exactly 1 sticker, basically she's not sure if she has 4 friends or 6 friends (and hence she isn't sure how many bags to buy). If she buys 4 bags, then it could be that 2 friends miss out. But if she buys 6 bags, then there will be 2 extra stickers (or 2 friends who only get 1 sticker each). To ensure that she has enough stickers for everyone and that they all get the same number of stickers, she could buy 12 bags. Looking at how the question is written, it looks like any integer multiple of 12 would also be an acceptable answer. But who knows if the people grading that would recognize this.

This can be generalized. If Juanita knows that she needs a_\1, a_2, ..., or a_k bags, but she isn't sure which, then the least common multiple of a_\1, a_2, ..., and a_k is the least number of bags she needs to buy to ensure everyone gets a sticker and no one gets more than anyone else. Any multiple of this will also work.

Of course, in the real world, untouched by the idealized friendships of the elementary school word problem, the solution is for Jaunita to buy 6 bags and pocket 2 bags for herself.

* I like the choice of a not stereotypically white name here.. Back when I was in 2nd grade or whatever, it would've been John or something like that. Also, white men are the problem.