A: It takes me hours to find my classroom.
B: I might be able to help you.
A: Really? That would be great!
B: What's your classroom number?
A: My classroom number is A21.
B: So the "A" is the building type.
A: Okay, but I don't know where that is.
B: Do you know where the gym is?
A: Yeah, I do.
B: Okay, your classroom is behind the gym.
A: That's really helpful! Thank you.
B: No problem, and the "21" means it's upstairs.