Explications étape par étape:

1) 2(x - 7) = (2×x).- (2×7) = 2x - 14

3(-x + 1) = (3×-x) + (3×1) = -3x + 3

2) 2x - 14 = -3x + 3

2x + 3x = 3 + 14

5x = 17

x = 17/5