answer all questions with explanation

4. A chemist wants to compare four treatments using experimental mate- rial coming from the four manufacturers which routinely supply his company. There is sufficient experimental material from each manufacturer for 12 experimental units. Thus, three experimental units from each manufacturer are randomly assigned to each treatment. (a) State the appropriate mathematical model and all of its assumptions for this experimental situation. (b) State the sources of variation and their associated degrees of freedom for the ANOVA of the experimental data. (c) Briefly describe how inferences about the main effects of treatments in the resulting ANOVA may be affected by the significance or lack of significance of the interaction term in the ANOVA. (d) Briefly describe how you would investigate differences among the treat- ments if the main effect of treatment in the resulting ANOVA is significant