Quelqu’un pourrait m’aider avec cet exercice s’il vous plaît ou même juste m’expliquer parce que je ne comprends absolument rien. Merci d’avance

At the "no mutants allowed" country farm, every sheep has 4 legs, every chicken has two legs, and all animals have only 1 head. asked to count how many sheep and chicken are in the fields, a farm boy reports back that there are 140 feet and 50 heads. how many sheep and chicken are there? there are sheep and chicken at the farm.