"Chairs of teachers" is awful english. Literally correct but not how you would say that sentence in english. "The teachers' chairs" is better
It accepted it for me, but it didn't like the apostophe and told me I was "almost correct" ... I've made a report about it.
"The chairs of the teachers" would also work while preserving the parallel word order.
I wrote "The chairs of the teachers" which was still marked as incorrect. The correct answer offered was "Chairs of the teachers". I'll report it again.
Guys, I'd strongly discourage the approach of saying, 'The chairs of the teachers'. For example, how often when you speak do you say 'The car of my father'? Or...'The phone of my brother'?
Yes, you are actually correct. But it's more natural, simple, convenient, and easily understood when you say 'My father's car', 'My brother's phone'.