Market research was conducted for a national retail company to compare the relationship between sales and advertising during the warm spring and summer seasons as compared with the cool fall and winter seasons. The data shown in the following table were collected over a period of several years.

a. Identify a single regression model that uses the data for both warm and cool seasons and that defines straight-line models relating sales revenue (Y) to advertising expenditure (X) for each season.
b. Using the computer output given next, determine and plot the fitted straight lines for each season.
c. Test whether the straight lines for cool and warm seasons coincide.
d. Test H0: "The lines are parallel" versus HA: "The lines are not parallel."
e. In light of your answers to parts (c) and (d), comment on differences and similarities in the sales-advertising expenditure relationship between cooler and warmer seasons.
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