Global warming is a major issue, and CO₂ emissions are an important part of the discussion The article “Effects of Atmospheric CO₂ Enrichment on Biomass Accumulation and Distribution in Eldarica Pine Trees” (J. Exp. Bot. 1994: 345 349) describes the results of growing pine trees with increasing levels of CO₂ in the air. Here are the observations with x = atmospheric concentration of CO₂ (parts per million) and y = mass in kilograms after 11 months of the experiment.

a. Explain why s_Ŷ is larger when x = 750 than when x = 600.
b. Calculate a confidence interval with a confidence level of 95% for the true average mass of all trees grown with a CO₂ concentration of 600 parts per million.
c. Calculate a prediction interval with a prediction level of 95% for the mass of a tree grown with a CO₂ concentration of 600 parts per million.
d. If a 95% CI is calculated for the true average mass when CO₂ concentration is 750, what will be the simultaneous confidence level for both this interval and the interval calculated in part (b)?

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X 408 408 554 y 1.1 1.3 1.6 554 2.5 680 680 812 812 3.0 4.3 4.2 4.7