What's (-3x + 7) + (-6x + 9) and if you can, ow do I show work for that

In order to add the two expressions (-3x+7) and (-6x+9), you combine the like terms, or the terms with the same variable and are raised to the same power. Because - 3x and - 6x are like terms, you can add those together to result in - 9x. Then, because 7 and 9 are like terms, you combine those to get 16. Because - 9x and 16 are not like terms, your answer will remain as:

-9x+16