Among 25 silver dollars struck in 1903 there are 15 from the Philadelphia mint, 7 from the

Question:

Among 25 silver dollars struck in 1903 there are 15 from the Philadelphia mint, 7 from the New Orleans mint, and 3 from the San Francisco mint. If 5 of these silver dollars are picked at random, find the probabilities of getting
(a) 4 from the Philadelphia mint and 1 from the New Orleans mint;
(b) 3 from the Philadelphia mint and 1 from each of the other 2 mints.