6.3 Analyze the carbohydrate data in Table 6.3 using appropriate software (or, preferably, repeat the analyses using several different regression programs and compare the results).

a. Plot the responses y against each of the explanatory variables x1,x2 and x3 to see if y appears to be linearly related to them.

b. Fit the Model (6.6) and examine the residuals to assess the adequacy of the model and the assumptions.

c. Fit the models