5) gitl says, “laughter is our only weapon.” what does she mean?
from the devils arithmetic
answer only if you have read the book

“The human race has only one really effective weapon and that is laughter.”
- Mark Twain

“Wit is a dangerous weapon, even to the possessor, if he knows not how to use it discreetly”
- Michael de Montaigne

It basically means that we weren't brought into this world to be sad. "Laughter Is Our Only Weapon" means that laughter is what is gonna bring joy and a happy spirit back. Laughter will cut through someone trying to bully you. If you just laugh and stay happy. Your weapon has done it's job and so have you.

She means that when someone laughs they get weak

Neither don’t use either

Because she’s in school