Answer: 9
Step-by-step explanation:
In order to make the expression a perfect square, ,we ate going to add to the expression the square of the half of the coefficient of 6.
x² + 6x + c
= x² + 6x + (6/2)²
= x² + 6x + 3²
= x² + 6x + 9
Therefore, 9 is the required solution that will.make the expression a perfect square.