13.4 Interpreting slopes on average monthly visitor satisfaction Refer to the previous exercise.

a. Explain why setting x2 at a variety of values yields a collection of parallel lines relating yn to x1. What is the value of the slope for those parallel lines?

b. Since the slope 0.55 for x1 is larger than the slope 0.0015 for x2, does this imply that x1 has a larger effect than x2 on y in this sample? Explain.