5x - 11 = 29
5x = 29 + 11
5x = 40
x = 40 : 5
x = 8
x + 5273 = 5723
x = 5723 - 5273
x = 450
x : 9 = 12
x = 12 · 9
x = 108
21 - 3x = 6
3x = 21 - 6
3x = 15
x = 15 : 3
x = 5
13x(x - 2) - 2x = 7
13x(x - 2) = 7 + 2x
13x^{2} - 26x = 7 + 2x
13x^{2} = 7 + 28x
13x = 7 + 28
13x = 35
x = 35 : 7
x = 5