Question

How do you check that the solution to `2(5 - 2z) = 20 - 2(z - 1)` is -5?

Answer 1

I'm afraid it's not. Expanding:
`2(5−2z)=10-4z`
and
`20−2(z−1) = 20-2z+2`
Now we can bring all the variables on the left, and all the numbers to the right:
`-2z=20-10+2`
which yelds
`-2z=12`
and thus `z=-6`