How do you find out how many comboinations of a group?

I'm doing a hspa prep packet and one of the questions is " the track coach needs 4 runners. her choices are Alex, Bryon, Chris, Daryl, Eddie, and Frank, How many different four person relay teams can be made from there six?" I'm pretty sure theres some type of equation to use but i can't remember it. Please don't give me the answer if possible. Thank you.