The pull strength of a wire bond is an important characteristic. The following table gives information on pull strength (y), die height (x1), post height (x2), loop height (x3), wire length (x4), bond width on the die (x5), and bond width on the post (x6).




(a) Fit a multiple linear regression model using x2, x3, x4, and x5 as the regressors.
(b) Estimate σ2.
(c) Find the se (Bj). How precisely are the regression coefficients estimated, in your opinion?
(d) Use the model from part (a) to predict pull strength when x2 = 20, x3 = 30, x4 = 90, and x5 = 2.0.

X6 29.6 8.0 5.2 19.6 94.9 2.1 2.3 8.3 89.7 5.2 19.8 32.4 2.1 1.8 5.8 8.5 19.6 31.0 96.2 2.0 2.0 8.8 95.6 2.1 6.4 19.4 32.4 2.2 9.0 5.8 28.6 86.5 2.0 18.6 1.8 9.3 5.2 30.6 84.5 2.1 2.1 18.8 20.4 88.8 9.3 5.6 32.4 2.2 1.9 9.5 6.0 19.0 32.6 85.7 2.1 1.9 9.8 5.2 20.8 32.2 93.6 2.3 2.1 2.1 10.0 5.8 19.9 31.8 86.0 1.8 10.3 6.4 18.0 32.6 87.1 2.0 1.6 10.5 6.0 20.6 33.4 93.1 2.1 2.1 10.8 6.2 20.2 31.8 83.4 2.2 2.1 20.2 11.0 6.2 32.4 94.5 2.1 1.9 11.3 6.2 19.2 31.4 83.4 1.9 1.8 11.5 5.6 17.0 33.2 85.2 2.1 2.1 11.8 6.0 19.8 35.4 84.1 2.0 1.8 86.9 12.3 5.8 18.8 34.0 2.1 1.8 12.5 5.6 18.6 34.2 83.0 1.9 2.0