a) 4x + 12 + 15x + 15 = 6x + 9 + 7x + 28 + 8
19x - 13x = 45 - 27
6x = 18
x = 18 : 6
x = 3
b) 10x - 15 + 16x + 28 - 48 = 6x + 3 + 4x + 12 + 30
26x - 10x = 35 + 45
16x = 80
x = 80 : 16
x = 5
c) 15x + 70 + 8x + 52 - 15 = 20x + 48 + 2x + 76 - 11
23x - 22x = 107 + 113
x = 220
d) 36x - 27 - 21x - 35 = 15x + 50 - 8x - 60 - 4
15x - 7x = 62 - 14
8x = 48
x = 48 : 8
x = 6
e) 2x² + 2x - 3x - 12 = 2x² - 6x + 8
2x² - x - 2x² + 6x = 12 + 8
5x = 20
x = 20 : 5
x = 4