There are seven runners in a race. They all finish the race, and no two runners finish the race at the same time. Find:

a: the number of ways that the runners can finish the race.

b: the number of ways, in order, that the first three runners could finish the race.

c: the number of ways, regardless of order, that the first three runners could finish the race.

For a, I think its just 7!. But I don't understand what is the difference between b and c.