4) The two different lines for the two headquarters are: Full model: Y = 0 + 1X1 + 2X2 + Reduced model: Y = 0 + 1X1 + Explanation of how the diagram is drawn and how it looks like: The full model has different slopes for employees in the two countries, while the reduced model has the same slope for employees in the two countries. The difference in the slopes is due to the difference in the intercepts. It is drawn such that the y-intercept is at 0 + 2 for the full model, and 0 for the reduced model. The x-intercept is at -1 for both models. The slope is 1 for both models.

5) If we suspect that for the two headquarters, the regressions may have different intercepts and slopes at the same time, then the answers to the above questions 1), 2), 3) and 4) would differ. For question 1), the full model would be: Y = 0 + 1X1 + 2X2 + 3X3 + And the reduced model would be: Y = 0 + 1X1 + 2X2 + For question 2), the full model would have different slopes for employees in the two countries, while the reduced model would have the same slope for employees in the two countries. The difference in the slopes would be due to the difference in the intercepts. For question 3), the null hypothesis would be that the slopes are the same in the full and the reduced models. The alternative hypothesis would be that the slopes are different in the full and the reduced models. For question 4), the two different lines for the two headquarters would be: Full model: Y = 0 + 1X1 + 2X2 + 3X3 + Reduced model: Y = 0 + 1X1 + 2X2 + The full model would have different intercepts for the two headquarters, while the reduced model would have the same intercept for the two headquarters. The difference in the intercepts would be due to the difference in the slopes.