Bonjour,
2x + 4x + 12x = 144
18x = 144
x = 144/18
x = 8
2x + 4x + (4x + 40) = 520
2x + 4x + 4x + 40 = 520
10x = 520 - 40
10x = 480
x = 480/10
x = 48
8x + 10 = 10x + 4
8x - 10x = 4 - 10
- 2x = - 6
x = 6/2
x = 3
10x - 14 = 16x - 26
10x - 16x = - 26 + 14
- 6x = - 12
x = 12/6
x = 2