6x^2 + 12x - 9x^3
I am going to assume that you want to know how to factor it because those cannot be added or subtracted.
In order to factor, we see what goes into all three of the numbers. We see that 3 goes into all three of the numbers so now we write it like this:
3(2x^2 + 4x - 3x^3) BUT we can still see that each of the numbers has at least one x attached to it so we can also factor that out. We then write this:
3x(2x + 4 - 3x^2) and that is it factored.