hi cookiepie,
try tis method
total animal = 12
birds - 2 legs, rabbits - 4 legs
rabbit has 36 more legs than all birds, so it 36/4 - 9 rabbits
so u start with 9 rabbits and 3 birds
take that to check if the rabbit has 36 more legs than bird
9x4 = 36, 3x3 = 9, 36-9 = 27, rabbit...