Question

Cows have 4 legs, chickens have 2 legs, so
cows ---x , chickens ---- y
4x + 2y = 148
2x + y = 74
y = 74 - 2x

Could you tell me where the 74 come from I still do not understand it

Answer 1

well, it has to be 4 x + 2 y = some number of legs :)
if it is 148
then
4 x + 2 y = 148
divide that equation by 2
2 x + 1 y = 74 sure enough, same thing
subtract 2 x from both sides
y = 74 - 2 x
still the same
In other words for any chosen number of legs, like 148, those equations are all valid and the same.