Consider the inverter data in Exercise 12-66. Delete observation 2 from the original data. Define new variables

Question:

Consider the inverter data in Exercise 12-66. Delete observation 2 from the original data. Define new variables as follows:
And

(a) Fit a regression model using these transformed regressors (do not use x5).
(b) Test the model for significance of regression using a = 0.05. Use the t-test to investigate the contribution of each variable to the model (a = 0.05). What are your conclusions?
(c) Plot the residuals versus and versus each of the transformed regressors. Comment on the plots.