a farmer has sheep,horses and chicken. the number of horses is double the number of sheep. the number of chicken is 3 times the number of sheep. the animals hav

you have to choose your informations :
s for the numbe of sheep (mouton)
h for the number of horses (cheval)
c for the number of chicken (poulet)

h=2*s
c=3*s
4*h+4*s+2*c = 36 legs (jambes)

if you replace h and c by its value :  8s+4s+6s= 36 
you find s=2
and h=4
and c=6

in the farm, there are
2 sheep
4 horses
6 chicken