If you are asking if your work is good,thn yes,you are right
The inequality that represents the domain of the function is 
<h3>How to determine the domain?</h3>
The function is given as:

Set the radicand greater than or equal to 0

Multiply through by 2
x - 20 ≥ 0
Add 20 to both sides
x ≥ 20
Hence, the domain of the function is x ≥ 20
Read more about domain at:
brainly.com/question/1770447
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from x15 to x 25 is 4 - -16 = -20 degree change
25 -15 = 10000 feet
-20/10 = -2 degrees every 1000 feet