All employees with their name, job title, salary and its salary class difference. The latter will give information per employee if their salary is above (signify +) or below (signify -) the average of the salary set for the job (see min_salary and max_salary).

SELECT 
  e.employee_id, 
  e.first_name, 
  e.last_name, 
  j.job_title, 
  e.salary,
  CASE WHEN salary>AVG(salary) THEN max_salary - min_salary END AS salary_class_difference
FROM hr.employees e, hr.jobs j
WHERE e.job_id=j.job_id;

This is the best I could come up with.

Sample Database