Coucou !
Exercice 1
9x = 3x + 12
= 9x -3x = 3x + 12 -3x
= 6x = 12
= 6x/6 = 12/6
= 2
15x = 12x + 42
=15x - 12x = 12x + 42 - 12x
=3x = 42
=3x/3 = 42/3
= 14
