12.23 The results from a regression model analysis are shown as follows:

yn = -61.50 + 21.8x1 12.12

+ 23.7x2 122.42

- 15.4x3 132.42 R2 = 0.74 n = 25 The numbers below the coefficient estimates are the sample standard errors of the coefficient estimates.

a. Compute two-sided 95% confidence intervals for the three regression slope coefficients.

b. For each of the slope coefficients, at the 5% level of significance, test the hypothesis H0 : bj = 0