(a) Use an appropriate computer program to fit a plane to the following data relating the monthly water usage of a production plant (gallons) to its monthly production (tons), mean monthly ambient temperature (°F), and the monthly number of days of plant operation over a period of 12 months.

(b) Estimate the water usage of the plant during a month when its production is 90.0 tons, the mean ambient temperature is 65°F, and it operates for 20 days.

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