I answered "heeft u jurken en jassen".
"U" is formal for you(singular). I don't know why it is heeft and not heb because u and je usually have the same conjugation (but u usually keeps the t at the end of the verb when it's a question)
You could say hebben jullie to a single person when for instance it is an employer in a clothing store. The jullie refers to the shop / company then. But it wouldn't be specifically formal. That would be heeft u.