3х-64=125
3х=64+125
3х=189
х=189:3
х=63
5x/6 -b=1/3
5x-6b=6/3
5x=2+6b
x=(2+6b)/5
x>0, (2+6b)/5>0, 2+6b>0 ⇒6b>-2 ⇒b>-1/3
ответ:b∈(-1/3;+∞)
-5x - 9 = -6
-5x = -6 + 9
-5x = 3
x = 3 : (-5)
x = - 3/5
x = -0,6
-2x - 3 = 1
-2x = 1 + 3
-2x = 4
x = 4 : (-2)
x = -2
10x + 1 = 6x
10x - 6x = -1
4x = -1
x = -1 : 4
x = -0,25