Let's call cows x, and chickens as y.
Cows have 4 legs
Chickens have 2 legs.
Let's make two equations from the information they gave us!
x + y = 42
4x + 2y = 114
Now, let's multiply the first equation by 4.
4x + 4y = 168
4x + 2y = 114
Now, subtract the second equation from the first one.
4x - 4x + 4y - 2y = 168 - 114
4y - 2y = 168 - 114
2y = 54
y = 27
Now, plug y = 27 into either equation and solve for x.
x + y = 42
x + 27 = 42
x = 42 - 27
x = 15
There are 15 cows and 27 chickens.
