"There are six desks."
I think you can say 六つつくえがあります, but I'm not sure. Maybe someone could clarify it better :)
I had the understanding that if the count precedes the noun, the particle joining them is ALWAYS の:
六つの つくえが あります
can someone confirm, or correct me on this?
DuoLingo hasn't taught us that construct yet
(count + の + noun + particle + rest of sentence).
It is currently focusing on:
が (non は particle - in these sentences it will always be always が, but later we will learn sentences that require a different particle)
..... (rest of sentence)
The prononciation changes when we use pieces counting "つ" See the site in the tips section of the lesson