1. A laundry detergent manufacturer wished to test a new product prior to market release. One area of concern was the relationship between the height of the detergent suds in a washing machine to the amount of detergent added and the degree of agitation in the wash cycle. For a standard-size washing machine tub filled to the full level, different agitation levels (measured in minutes) and amounts of detergent were assigned in random order, and sud heights measured. Open the Detergent.sas7bdat data in SAS and answer the following questions. (SAS is done and graphs are uploaded for each part, just need explanations and answers based on the graphs) Use the residual plots to examine the plausibility of the model assumptions. By examining the residual plots, can you find reasons to suspect that a linear model is not adequate? If so, what other terms would you consider adding to the model? Explain how you reached your conclusion.

a. By examining the plot of height (y), against agitation (x₁) at each value of amount (x₂), suggest a multiple regression model to explain the variation in sud height.