In the development of coatings (such as for paper, optical lenses, computer screens, etc.) a researcher will often study a "thin film"; that is, the coating cured on some substrate such as glass; rather than studying the coating cured on the actual product. The data set thinf ilm .txt contains data from a study of thin films made on two different substrates: glass and foil.

(a) What rationale do you think is behind studying a thin film as opposed to the entire product?

(b) Make scatter plots for both the glass and foil portions of the data to study the relationship between the formulation component and the max load (a measurement of the strength of the coating).

(c) Describe how the max load is affected by the amount of the formulation component and how the substrate affects that relationship.