Use the following information from a multiple regression model:

n = 20 b₁ = 4 b₂ = 3 S_bi = 1.2 Sb₂ = 0.8

a. Which variable has the largest slope, in units of a t statistic? 

b. Construct a 95% confidence interval estimate of the population slope, b₁. 

c. At the 0.05 level of significance, determine whether each independent variable makes a significant contribution to the regression model. On the basis of these results, indicate the independent variables to include in this model.