18 - 2[x + (x-5)]
First I would get rid of the inside parenthesis by distributing the + to everything inside and end up with;
18 - 2[x + x - 5]
Then I'd combine like terms inside the brackets
18 - 2[2x - 5]
Then I'd multiply what is inside the brackets by the -2
18 - 4x + 10
I'd combine like terms and end up with:
28 - 4x......or rewritten as -4x + 28