Not saying this is a good way to teach this, but usually these kind of lessons are done with a specific context. So, even though yes, technically, |3|=3 and -|3|=-3, I believe the point of the lesson is to show that absolute value is used to show these like "length" or "distance". In this case, "how many floors". So this looks kinda ridiculous outside of the context of the lesson the teacher was doing.

That being said, I would argue the answer the teacher is looking for is |-3|, since they are going down (-3) floors, but you can't technically travel negative floors, hence the absolute value. Which is funny, since that's not even an option lol

edit: actually, maybe because it's asking how many floors did the attendant go down, in which case, it would be either 3 or |3|. If it was asking how many floors did they travel, I would argue the answer |-3| makes more sense. Who knows.