Exercice 23 et 24 urgent svp

bonjour

a = 48 + 8 x
b = 35 - 7 a
c = 12 x - x y
d = 15 x + x b

a) 12 x + 216
b) 12 x + 18
c) 12 x + 18
d) 18 x + 12