The price for a half$-$page newspaper ad is $$20,000.$ The newspaper bills the agency, and the agency in turn bills the client for the $$20,000.$ The client pays that amount to the agency, and the agency sends $$17,000$ to the newspaper, keeping $15\%($$$3,000)$ for itself. This $15\%$ that the agency keeps is called the agency's Blank$\_\_\_\_\_\_.$

Multiple choice question.

incentive fee

markup

media commission

retainer