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