hello!
so the answer that you put there is actually wrong and i'll tell you why and how to do it
so since you are adding the two:
-8x + 9x = x (so you got this part right)
-12 + 4 = -8 (this is where you got it wrong, -12 added 4 goes up in value to -8)
so the final answer is x - 8
i hope this helped and have a nice day!
