Consider the regression in equation (13.20).

(a) Demonstrate, either with confidence intervals or two-tailed hypothesis tests, that

a, bâ•›1, and bâ•›2 are statistically significant.

(b) Verify the predicted earnings at ages 30, 40, 50, and 60.

(c) Use equation (13.22) to verify that maximum predicted earnings occur at approximately 46.67 years of age.