I'm sure a lot of people have seen questions like this one. I've gotten half of it done, but I could use a hand with the other half.

A large box contains 10 pairs of shoes. If 6 shoes are selected at random, what is the probability of:

a) no complete pairs

My answer:

b) exactly one complete pair

My answer:

c) exactly two complete pairs

d) exactly three complete pairs

I could use a hand with the latter two.