Hello, I am having trouble on one of my homework problems at my university. It involves binomial and multinomial coefficients. The problem goes as following:

Suppose that an airport food court has three restaurants: Subway, Burger King, and Mcdonalds.

if subway is closed and each customer is equally likely to go to either Mcdonalds or Burger King, what is the probability that six of the next nine customers go to Burger King and three of the nine go to Mcdonalds?

Right now I am stuck in how to approach the problem. I was thinking to start with 9*9 possibilities of each customer going to either restaurants. Am I on the right track? What else do I need to consider and think about?

Help is is greatly appreciated!