2x-x+9
First, you would group your like terms together by circling them.
(2x)(-x)+9
Pretend the parentheses are circles.
Your -x will act as -1x because if you ever see a +x or -x there is always an invisible 1 there.
Next you would do like you would normally do to subtract something except you just have x right there. 2-1 is 1. So 1x.
Lastly, you put 9 and 1x together, so therefore your answer will be 1x+9, or x+9. I tried my best to explain this and I really hope it helped.