The quality control director for a clothing manufacturer wants to study the effect of operators and machines on the breaking strength (in pounds) of wool serge material. A batch of the material is cut into square-yard pieces, and these pieces are randomly assigned, 3 each, to each of the 12 combinations of 4 operators and 3 machines chosen specifically for the experiment. The results, stored in Breakstw. are as follows:

At the 0.05 level of significance,
a. Is there an interaction between operator and machine?
b. Is there an effect due to operator?
c. Is there an effect due to machine?
d. Plot the mean breaking strength for each operator for each machine.
e. If appropriate, use the Tukey procedure to examine differences among operators and among machines.
f. What can you conclude about the effects of operators and machines on breaking strength? Explain.
g. Repeat the analysis, using machines as the only factor. Compare your results to those of (c), (e), and (f).