Subtract x from both sides canceling out the x on the left, getting...
-4 = x + 1
Then subtract the 1 from both sides canceling out the 1 on the right, getting...
-5 = x
Subtracting x from 2x gets you 1x which you just write as x because there is only one x. Doing the equation from the other side will still get you the same answer and I will show you.