Question: Binomial-solution, need help.. probably easy.

Hello people, Recently I recieved some help with binomial-solutions. I will most likely come with more questions while I'm working my way through my homework. In a bag there are 4 red marbles, 5 blue balls and 6 white balls. We select randomly and simultaneously 3 balls from the bag. What is the probability for each of the following events; a) The 3 balls have different colors. I did: binomial(4, 1)*binomial(5, 1)*binomial(6, 1)/binomial(15, 3) b) The 3 balls are all the same color. I did: (binomial(4, 3)+binomial(5, 3)+binomial(6, 3))/binomial(15, 3) c) The 3 balls consist of 2 of the same color and 1 of a different color. This is the one I cannot figure how to make. Anyone? (:
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