A firm with a nationwide system of bus facilities wants to develop a regression model that can explain its profit Y,measured in thousands of dollars per year, by its annual sales of bus repair and maintenance services (X₁), its annual sales of bus equipment (X₂), and its annual sales of bus advertising panels (X₃). A random sample of 12 of its facilities yields these results (standard errors are in parentheses):

The error sum of squares is 879.5; the total sum of squares is 5,981.3.

(a) Comment on the significance of the regression coefficients.

(b) Comment on the overall significance of this regression.

(c) Do you see evidence of a possible violation of crucial assumptions?

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= -2.29.0279X +.0885X2 + 3.753X3 (13.65) (1439) (.0161) (2.402)