This isn't the coding that is eluding you.. it's the math. This is a standard combination problem. I think you should look at Dr. Math's Lovely Permutation and Combination FAQ to get handle on what you are trying to do.

Now that you have read that... I think you are trying to do a 4 choose 3 combination. buying a linear algebra or discrete math book may help you here. ... at least that's where I learned about it.