Every year, air traffic controllers are given a test of their job performance based on a computer simulation. Test scores, which range from 0 to 100, are considered a good indicator of actual job performance, so there is great interest in the determinants of these scores. For a random sample of 1000 air traffic controllers, test scores are regressed on years of experience in this profession (X1) and years of college education (X2). The results are shown below:
 = 15.0 + 3.1X1 + 4.2X2
sb = 1.4 1.8
R2 = .68 Sy|x = 2.2
Based on these results, answer the following questions:
(a) For each additional year of college education, what is the expected effect on test scores?
(b) For each additional year of experience as an air traffic controller, what is the expected effect on text scores?
(c) How strong a relationship is indicated by the regression?
(d) What is the expected test score of a graduate of a four-year college who has 21 years of experience as an air traffic controller?