Just answer in any honest way and it will work out...because that way you and they can be on the same page if you are hired. You want a boss who would support your own way of handling it.
My own answer would be:
"Because I believe that coworkers who cooperate and trust one another are better for the company, I would talk to the erring employee first. I would be tactful but firm in saying this was not acceptable behavior. I would remain very alert, and if I noted any more questionable behavior, I wouldn't hesitate to go to my supervisor about it.
You have to say what they want to hear. You'll report it to your supervisor, and to show sincerity you should say something along the lines of it hurting everyone because of the rising cost of insurance. It's the way of the world. You'll notice that in a court of law, both the judge and the attorney will advise you to plead "not guilty" whether you're guilty or not. Pleading "not guilty" when you know you're guilty is a lie, but it's a lie that is promoted by the legal system.