For the data in the last problem, use a computer to verify that a least squares regression line using only X values (age) less than 7 yields b1 = 0.247 and b0 = 3.51. Verify that when using only the X values great than 7 you get b1 = .009 and b0 = 4.8. What does this suggest about using a linear rule for all of the data?