The personnel director of the communications firm in Exercise 17.5 has just provided another variable describing the company’s technical sales representatives: their scores on a sales aptitude test they were recently given. Using data file XR17015, with y = average dollar sales per call, x1 = years of experience, and x2 = score on the sales aptitude test, fit a second-order model with interaction to the data. Interpret the R2 value for the model and indicate whether, at the 0.05 level, the model is significant.