Answer:

Step-by-step explanation:
Given that

We have slope of linear regression line is

So regression line would be of the form
(since it passes through xbar, y bar)

is the equation of regression line.
The two black circles represents "The selling prices that produces no profit." If the selling is 10, the profit is 0. If the selling price is 60, the profit is 0.
The selling price that provides the maximum profit is represented by the red dot. It is between the selling price of 30 and 40. Its maximum profit is equal to 12,000.