A process engineer designed a study to evaluate the differences in the mean film thick-nesses of a coating placed on silicon wafers using three different coating processes. From a batch of 30 homogeneous silicon wafers, 10 wafers are randomly assigned to each of the three processes. The film thickness (y) and the temperature (x) in the lab during the coating process are recorded on each wafer. The engineer is concerned that fluctuations in the lab temperature have an effect on the thickness of the coating. The data are given here.

a. Plot the thickness of the coating versus the temperature in the lab.
b. Do the thickness and temperature appear to be linearly related for each of the three processes?
c. Write a model relating the thickness of the coating to the coating process with adjustments for the temperature in the lab during coating.
d. Use a computer program to fit the model in part (c).

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