3(2-3х) (-1)+7(4-2х)=12

6-9x+1+28-14x=12
35-23x=12
-23x=-23
x=1

3(2-3x)(-1)+7(4-2x)=12
(6-9x) (-1)+28-14x=12
-6+9x+28-14x=12
-5x=12-28+6
-5x=-10
x=2