Answer:
The number to add is (11/2)^2 = 121/4
Step-by-step explanation:
Here, we want to know the number that will complete the square
We rewrite the equation as follows;
x^2 + 11x = -30
x^2 + 11x + (11/2)^2 = -30 + (11/2)^2
x^2 + 11x + 121/4 = -30 + 121/4