15-10x+20+12x=4x+7
35-10x+12x=4x+7
35+2x=4x+7
2x+35=4x+7
2x+35-35=4x+7-35
2x=4x-28
2x-4x=4x-28-4x
-2x=-28
-2x/-2=-28/-2
x=14
15-10x+20+12x=4x+7
35-10x+12x=4x+7
35+2x=4x+7
2x+35=4x+7
2x+35-35=4x+7-35
2x=4x-28
2x-4x=4x-28-4x
-2x=-28
-2x/-2=-28/-2
x=14