The answer is stratosphere...
The value of the unknown number is 10.5.
Let the unknown number = x
When 20 is subtracted from the number and the result is squared which is equal to the square of the unknown number minus 20:
(x - 20)² = x² - 20
<em>expand the equation;</em>
x² - 40x + 400 = x² - 20
<em>collect similar terms together;</em>
x² - x² - 40x = -20 - 400
-40x = -420

Thus, the value of the unknown number is 10.5.
Learn more about word problem here: brainly.com/question/18336356
<span> carbohydrates, lipids, proteins, and nucleic acids.
Hope this helped!</span>
A. The population continues to grow