Scenario 3 A manager for a large software company wants to study the factors that affect her company's sales across different regions of the US. A recently collected database contains a random sample of 135 sales regions. For each of these regions, data is available on the region's sales (Y, in dollars), the average price in that region (X1, in dollars), average marketing expenditures in that region (X2, in dollars), and the median household income level for the region (X3). Median household income level is coded as X3=O ifincome level is low, and X3=1 if it is high. The manager has several conjectures about the company's sales. Using the variable notations Y, X1, X2 and X3, you are asked to construct and interpret a regression model that enables the testing of the manager's conjectures