Think slightly at abstract level.
x bar = x+1
meaning "anything" bar = "anything" +1;
In other words whatever you want to find the bar for, just add 1.
y bar = y + 1
2y bar = 2y + 1
2x bar = 2x + 1
(x^2) bar = (x^2)+1
Hope this helps.
Don't You think 2X bar = 2(x + 1) here rather than 2x + 1 or 2x + 2 as it says wherever you have x bar replace it with x + 1.
I am still confused.