You know right off that chickens have 2 legs and rabbits have 4 legs.
If all 22 legs belonged to chickens, then there would be 11 animals, since 2 X 11 = 22.
But there were only 8 animals.
That means you'll need to trade in some chickens for rabbits.
Trade your chickens in two at a time (so you're exchanging 2 chickens for 1 rabbit).
You might try drawing a picture to help you see when you have 8 eight animals with a total of 22 legs.