Explications étape par étape:

b. x + 4 = x + 8

- x - 8 -x -8

0 = x -

c. 5x + 4 = 10x +8

-10x - 4 -10x -4

- 5x = 4

-5x ÷ -5 = 4 ÷ 5 = 0,8

x = 0,8

d. 15x + 4 = 5x + 4

- 5x -4 -5x - 4

10x = 0

10x ÷ 10 = 0 ÷ 10 = 0

x = 0