Question 486233
First off, you got the final sign wrong, it's -7.
You need to expand the (x+1)^2 and collect terms:
x^2 +6x -(x^2 + 2x + 1) -7 = 0
Collect terms again (you do it too):
4x - 8 = 0 
More little steps for you results in:
x = 2