You need to 1st group the expression as follows since you want to have a perfect square INTEGER/VARIABLE to the UTMOST right-side of the expression:
Now, we use the "ac" method for the first grouped expression, which involves finding 2 INTEGERS that when MULTIPLIED gives us "+ 49", and when added, gives us "- 14."
These FACTORS are simply - 7 and - 7. We then get:, and finally: