There are more parts to the question: b) Determine the least-squares regression equation from the sample data. c) Plot the residuals against the explanatory variable age. Does a linear model seem appropriate on the basis of the residual plot? d) Are there outliers of influential observations? e) Assuming the residuals are normally distributed, test whether a linear relation exists between age and HDL cholesterol levels at the alpha=0.01 level of significance Set up a hypothesis test.