Answer:
8x - 8z.
Explanation:
Let's first rearrange 6x-3y-z+2x+3y-7z where all the x's are together, all y's together, and all z's are together:
6x +2x + 3y - 3y - z - 7z.
First we combine like terms.
6x + 2x ⇒ 8x
3y - 3y ⇒ 0
z - 7z ⇒ -8z.
Since the y's result in 0, we do not include them.
Therefore, our answer is 8x - 8z.