13.19 A multiple linear regression model involv- ing one qualitative and one quantitative independent variable produced this prediction equation: y= 12.6+0.54x1-1.2x1x2 + 3.9x

a. Which of the two variables is the quantitative variable? Explain.

b. If x, can take only the values 0 or 1, find the two possible prediction equations for this experiment.

c. Graph the two equations found in part

b. Compare the shapes of the two curves.