777, I'll do a post on my suggested approach. It's the best I've seen and has given me some monster returns.
But before doing so, it's worth listing the simple approaches.
1. Boxing N horses will require N x (N-1) x (N-2) x (N-3) combinations.
That is, IMO, not the way to take FFs.
2. Taking a rover of 1 horse with N others will require 1 x N x (N-1) x (N-2) x 3 combinations.
Thus, roving 1 horse with 6 others requires 1 x 6 x 5 x 4 x 3 = 360 combos.
3. Taking W horses to win, X horses to run 2nd, Y horses to run 3rd and Z horses to run 4th will require W x (X-1) x (Y-2) x (Z-3) combinations. Note that the horses on each line MUST be continued to the next line. Any other approach would be illogical.
As an example, 3 to win, 4 to run 2nd, 6 to run 3rd and 8 to run 4th, gives us 3 x 3 x 4 x 5 = 180 combos
These are the basics, but some might not understand them, so they're listed in detail.