Answer:
20 animals = x chickens (2 legs) + y horses (4 legs).
x+y=20 (total number of animals)
2x+4y=64 *total number of legs)
x+y=20
x+2y=32
If you solve this system of animal with 2 and 4 legs, you get 6 chickens and 14 horses
x=6
y=14
Try on your own!