i solved this way:
captain - 1 head 1 leg
remains 14 heads 40 legs
-1 human - 13 heads 38 legs
-1 human 12 heads 36 legs
-1 human 11 heads 34 legs
-1 human 10 heads 32 legs
-1 human 9 heads 30 legs
-1 human 8 heads 28 legs
-1 human 7 heads 26 legs
-1 human 6 heads 24 legs
now 24 is divisible by 6.
if we continue to remove heads/legs as if there were more humans, we would get to numbers that are not divisible by 4 when we have a specific number of heads..therefore, there must be 6 cats.
for the sake of making sure:
5 heads 22 legs
4 heads 20 legs
3 heads 18 legs
2 heads 16 legs
1 head 14 legs (mutant cat)
C is the answer