How many levels are there left for Diego W Roel to reach if he/she could go to the max level for his/her position?
max level for his position refers to max_lvl; job level refers to job_lvl; level left to reach the max = SUBTRACT(max_lvl, job_lvl)
SELECT T2.max_lvl - T1.job_lvl FROM employee AS T1 INNER JOIN jobs AS T2 ON T1.job_id = T2.job_id WHERE T1.fname = 'Diego' AND T1.minit = 'W' AND T1.lname = 'Roel'