(a) There are 15 skaters in the Olympic women's competition, including 4 Americans. The gold medal goes to first place, silver to second, and bronze to third. In how many ways can the medals be awarded to three of the 15 skaters?
(b) here are 15 skaters in the Olympic women's competition, including 4 Americans. The gold medal goes to first place, silver to second, and bronze to third. In how many ways can the medals be awarded to three of the 15 skaters, if exactly one of the Americans wins a medal?