An article in Concrete Research presented data on compressive strength xx and intrinsic permeability yy of various concrete mixes and cures. Summary quantities are nn = 14, yyii = 572, yyii 2 = 23530, xxii = 43, xxii 2 = 157.42, and xxiiyyii = 1697.80. Assume that the two variables are related according to the simple linear regression model. a. Estimate σσ2. b. Test for significance of regression using = 0.05. Can you conclude that the model specifies a useful linear relationship between these two variables?