Answer:
We should add 9 on the both sides of the given equation.
Step-by-step explanation:
Since, for making a perfect square on the left side of a quadratic equation,
We add the square of the half of the coefficient of x on both sides,
The given equation,

Here, the coefficient of x is 6,
Half of 6 = 3
Square of 3 = 9,
Thus, we should add 9 on the both sides of the given equation.
Verification :

