Bonjour,
a)
6
6+3 = 9
9*5 = 45
45 +21 =66
66-6 = 60
60/4 = 15
15 -6 = 9
b)
x
x+3
5x+15
5x+ 36
4x+36 = 4(x+9)
x+9
9