Casa tua ha delle scale?
Marziota sentence is confusing. Scale is in English and not Italian. Let me clear it up:
The Weighting Scale is La Bilancia
The Scale as in a measurement scale is Scala
As when scala means stairs or ladder it's just the most obvious option. If someone tell you
Porta la scala qui it's obviously a ladder, or can you move your stairs around your house?
In this sentence for example it's always* ladder, because if asking if your house has stairs that's exactly the question you ask.
Casa tua ha una scala?
*Exception: In a conversation about a house you are in, you might say this sentence to ask if the house has stairs, but I would not expect it. It's much better to ask Ha una scala?
Technically "Il Teatro alla scala" named for Santa Maria alla Scala, the church that the opera house replaced, which itself was named after Beatrice Regina della Scala of the Scaliger family, medieval nobility. What their connection to stairs is, I don't know, but their coat of arms has a ladder on it. https://en.wikipedia.org/wiki/Scaliger
Duolingo really should finally fix the slow voice saying "un" instead of "una." Despite what a poster below has written, the slow voice absolutely says "un scala." I know scala is feminine, so I got it right, as I am familiar with the error in pronunciation, having heard it for years.
"hai" is the second-person singular form of avere (to have), whereas "avete" is the second-person plural form of avere.
So if you're asking one person if they have a ladder, it's fine to say "hai una scala?", but if you're asking a group of people if they have a ladder, you would say "avete una scala?".
Hope this helps. The first table in this link might be useful: https://www.thoughtco.com/italian-verb-conjugations-avere-4093137