First, we want to distribute the 2z to what's in the parentheses:
[tex] 2z-(2z+6z)=48 [/tex]
Then we need to distribute the negative sign outside of the parentheses in order to make it easier to solve and combine like terms:
[tex] 2z-2z-6z=48 [/tex]
Now we combine like terms. The '2z' and '-2z' cancel each other out, so:
[tex] -6z=48 [/tex]
Then we solve for z by dividing by -6 on both sides:
[tex] z=-8 [/tex]
So now we know that z = -8.