1)
(7x - 42)/4 = (5x + 5)/3 - 3x - 6 ( теперь умножаем на 12)
3(7x - 42) = 4*(5x + 5) - 12*3x - 12*6
21x - 126 = 20x + 20 - 36x - 72
21x - 126 = -16x - 52
21x + 16x = 126 - 52
37x = 74
x = 74 : 37
x = 2
=============
2)
(3x - 24)/5 + (7x + 35)/6 = (28x + 6)/15 + 1/3 (умножим на 30)
6*(3x - 24) + 5*(7x + 35) = 2*(28x + 6) + 30*1/3
18x - 144 + 35x + 175 = 56x + 12 + 10
53x + 31 = 56x + 22
56x - 53x = 31 - 22
3x = 9
x = 9:2
x = 3
====================
3)
(6x + 15)/8 - (10x + 14)/3 = (7x - 105)/4 - 55/8 (умнож. на 24)
3*(6x + 15) - 8*(10x + 14) = 6*(7x - 105) - 24*55/8
18x + 45 - 80x - 112 = 42x - 630 - 165
-62x - 67 = 42x - 795
42x + 62x = 795 - 67
104x = 728
x = 728 : 104
x = 7