What is being informally tested here, and what is the hypothesis test?

What is being informally tested here, and what is the hypothesis test?

The Kenton Food Company is interested in testing which size of a new organic, whole-grain breakfast cereal is most appealing to consumers. The company experimented with releasing the product in different package sizes for a preliminary period before the product’s mass release. The Chief Data Scientist of Kenton developed a regression model relating package size (in ounces) to product sales volume (in dollars). The diagnostic plot below was obtained. use this information to answer the following questions.

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