Simple....
you have:
3x-9=7x+12
To even solve this....isolate the variable your are trying to solve for....
3x-9=7x+12
-3x -3x
-9=4x+12
-9=4x+12
-12 -12
-21=4x
Simplify.....
[tex] \frac{-21}{4} = \frac{4x}{4} [/tex]
[tex] \frac{-21}{4} =x[/tex]
Thus, your answer.
