12. Consider the population of 140 observations that are presented in Table P-12. The Marshall Printing Company wishes to estimate the relationship between the number of copies produced by an offset printing technique (X) and the associated direct labor cost (Y). Select a random sample of 20 observations.

a. Construct a scatter diagram.

b. Compute the sample correlation coefficient.

c. Determine the fitted regression line.

d. Plot the fitted line on the scatter diagram.

e. Compute the standard error of estimate.

f. Compute the coefficient of determination and interpret its value. g. Test the hypothesis that the slope, , of the population regression line is zero. h. Calculate a point forecast and a 90% prediction interval for the direct labor cost if the project involves 250 copies. i. Examine the residuals. Does it appear as if a simple linear regression model is appropriate for these data? Explain.