It's not solvable without additional data. I'd assume the question is either incomplete (copied or rememberd wrong), allows educated guess (100 balloons per box

It's not solvable without additional data. I'd assume the question is either incomplete (copied or rememberd wrong), allows educated guess (100 balloons per box sounds reasonable, Bob wouldn't by boxes of 1000 if he plans to use only a couple of dozen). Or the question's goal is to get shared as much as possible (Facebook likes, shares etc).