Svp j'ai besoin d'aider!

a)3x + 7 -7 =13-7
3x/3=6/3
x=2

A) 3x + 7 = 13
3x = 13 - 7
3x = 6
x = 6/3
x = 2

B) 4x - 5 = 2x + 9
4x = 2x + 9 + 5
(-2x) + 4x = 14
2x = 14
x = 14/2
x = 7

C) -5y + 7 = 6 + 2y
(-2y) - 5y = 6 - 7
2y + 5y = 1
7y = 1
y = 1/7

Le dernier trop compliqué pour moi ^^