Ok I am 18 and my cousin gave me a fun brain teaser question..lol i have no idea so do any of you?

Ok my lil cousin came home with this the other day and i still have no idea and I have tried everything. She said there are 20 animals they are all cows and chickens..There are 26 legs and I'm supposed to figure out how many cows and chickens there are so I am giving up though I am curious as the the answer does anyone know.