a. What fraction of the variation in salaries can be explained by the fact that some employees are older than others?
b. What salary would you expect for a 42-year-old individual?
c. Find the 95% confidence interval for the salary of a new individual (from the same population from which the data were drawn) who is 42 years old.
d. Find the 95% confidence interval for the mean salary of all 42-year-olds in the population.