There are 18 animals and 40 legs in all so lets see how many cows could be born. 4,8,16,12,24,28,32,36,40. so there could be 9 cows and now lets see on chickens 2,4,6,8,10,12,14,16,18,20,22,24,26, 28,30,32,34,36,38,40. so the could be 20 chickens so if u think. i think the ancewer is 30 chickens and 10 cowws