addendum, some combination problems too

A: a freshman has 4 exams to take with 10 examination periods avaialable. how many possible arrangements are there of his exam schedule?

B: from a group of 5 swimmers and 8 runners, an athletic contingent of 7 is to be formed. how many teams are possible if there are to be: b1) 2 swimmers, 5 runners and b2) at least 3 swimmers