The abrasive effect of a wear tester on a particular fabric was measured while the machine was run at six different speeds. Forty- eight identical 5- inch- square pieces of fabric were cut, with eight squares randomly assigned to each of the six machine speeds: 100, 120, 140, 160, 180, and 200 revolutions per minute ( rev/ 200revolu-tionsperminute (rev/min). 200revolu-tionsperminute (rev/min). The 200 revolu-tionsperminute (rev/min). The order of assignment of the squares to the machines was random, with each square tested for a 3- minute period at the appropriate machine setting. The amount of wear was measured and recorded for each square. The data appear in the accompanying table.
a. Plot the six mean wear values versus machine speed and suggest a model.
b. Fit the suggested model to the data.
c. Suggest which residual plots might be useful in check the assumptions underlying the model.

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Machine Speed (rev/min) Wear 100 120 140 160 180 200 23.0, 235,24.4,25.2,25.6, 26.1,24.8, 25.6 26.7,26.1,25.8,26.3,27.2, 279,283,274 28.0,28.4.27.0,28.8,29.8, 294, 28.7,29.3 32.7, 32.1,319, 33.0.33.5, 33.7, 34.0, 325 43.1, 41.7.424, 421, 43.5, 43.8, 44.2.436 54.2, 43.7,53.1, 53.8.55.6, 55.9, 54.7,54.5