Réponse :
Explications étape par étape :
x/7 = 3
x = 7 x 3
x = 21
5x + 1 = 9
5x = 9 - 1
5x = 8
x = 8/5
2 + 4x = 7 - x
4x + x = 7 - 2
5x = 5
x = 5/5 = 1
3x - 6 = 2x - 4
3x - 2x = -4 + 6
x = 2
5 ( 2y + 3 ) = y - 8
10y + 15 = y - 8
10y - y = - 8 - 15
9y = -23
y = -23/9