Explanation:
the way I understand it, this means in how many ways can we pick 2 of the 7 horses, when the sequence of these 2 horses matters, but the sequence of the remaining 5 horses does not matter (as they finishing tied or not even starting is in that sense the same thing).
so, we are looking for the permutations of 2 out of 7 elements.
that is
7! / (7-2)! = 7×6 = 42
there are 42 different ways for these 7 horses to cross the finish line in the described constellation.