A farmer has chickens and cows. You ask the farmer how many chickens he has, and how many cows he has. The farmer has 28 healthy animals, and they have total of 64 legs. How many of his animals are cows? Write an equation

Set the number of chickens as x and number of cows as y

so the farmer has total 28 animals

so x+y=28

you know that since the animals are healthy

chickens will have 2 legs and

cows will have 4 legs

the total number of legs are 64

so 2x+4y=64

since you want to find the number of cows

so from the first equation x+y=28

we will get another equation x=28-y

then plug into 2x+4y=64

2 (28-y) + 4y=64

56-2y+4y=64

56+2y=64

-56 - 56

2y=8

y=4