The number you would add to both sides of the equation to use the "Completing the Square" method would be 16.
Step-by-step explanation:
To find the number to add to both sides of an equation to complete the square, divide the first-degree term's coefficient by 2 and square your remainder. In this case, the coefficient of the first-degree term is -8. After dividing by 2 and squaring it, you'll get 16, so that is the number you must add to both sides of the equation in order to complete the square.
