Let Y = Sales at a Fast Food Outlet (1000's $x _ { 1 } =$

Let y = sales at a fast food outlet (1000's of $), $x _ { 1 } =$ number of competing outlets within a 1-mile radius, $x _ { 2 } =$ the population within a 1-mile radius (1000's of people), and $x _ { 3 }$ be an indicator variable that equals 1 if the outlet has a drive-up window and 0 otherwise. Suppose that the true regression model is $Y = 10.00 - 1.2 x _ { 1 } + 7.0 x _ { 2 } + 15.4 x _ { 3 } + \varepsilon$
a. What is the mean value of sales when the number of competing outlets is 2, there are 8000 people within a 1-mile radius, and outlet has a drive-up window?
b. What is the mean value of sales for an outlet without a drive-up window that has three competing outlets and 5000 people within a 1-mile radius?
c. Interpret $\beta _ { 3 } .$