Answer:
16
Step-by-step explanation:
Given x^2 + 16x = 18. Complete the square:
Take half of the coefficient of x (in other words, take half of 16) and square the result: we get 8^2 = 64.
Add 64, and then subtract 64 from x^2 + 16x + 64 = 18 + 64
Then (x + 8)^2 = 82. From this point on it's easy to find the roots, but we were not asked to do so.
The desired number is 64; note that it is (16/2)^2.
