Answer: D) a quadratic function since the points are symmetric about the line x = 30
Explanation:
Here, the given table,
Number of people 10 20 30 40 50
Profit per person 500 800 900 800 500
Since, when we plot the given point we found that,
About the line x = 30,
(10,500) is symmetric to (50,500)
And, (20,800) is symmetric to (40,800)
Also, with help of regression, we found that the function for the given point is,

Which is a quadratic function.
Thus, Option D) a quadratic function since the points are symmetric about the line x = 30 is correct.