Answer:
<h2>-40</h2>
Step-by-step explanation:

In the equation x is the feet of width.
If the original width is 2 feet, then X^2 = 2^2 = 4
If the width changes to 4 feet, then x^2 becomes 4^2 = 16
The change is 16 - 4 = 12
The answer should be B. $12 per foot.