The answer upstairs is correct, but it seems impossible to express it this way.

First of all, choose three of the six numbers (no repetition), so the number selection method is C36 (you can't type this formula, you should understand), that is, 6×5×4= 120.

Just arrange the selected numbers as 3×2× 1=6.

So the total number should be 120×6= 120 species.