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3. (30 points) Consider the regression model :4; = [30 + )61251 + + mm, = e where y is the observed values, 331, mack a series of nonstochastic predictors, B0, [31, \"-3161: unknown parameters, and e, a random error. d. Describe the standard procedure used to determine if one explanatory variable in a linear regression model is important. (Ho : 53' = 0). e. What variables impact the magnitude of the standard errors of the estimates 33', j = 1, ..., Is? How? I\". What is the coefcient of determination R2? How is it used