I'm stuck on this question. It is an expected value question involving marbles:

"We have 20 marbles in a bag: 17 red and 3 blue. We randomly pull three marbles without replacement. If we pull three red marbles, we pay $10. In any other case we receive $10 for every blue marble pulled. (1 blue gets $10, 2 blue gets $20....) What is the expected value of this game?

I'm thrown off by the third marble.