Answer:
están
Step-by-step explanation:
We want to find the form of estar that matches with ustedes. In other words, we want to conjugate estar to the ustedes form.
Estar contains the following conjugations:
yo estoy
tú estás
él/ella/usted está
nosotros estamos
vosotros estáis
ellos/ellas/ustedes están
As indicated, ustedes the third person plural conjugation -- which is están.