How much higher is James Johnson's salary from the minimum salary of his title?
James Johnson is the fullname of an employee; full name = firstname, lastname; minimum salary refers to minsalary; calculation = SUBTRACT(salary, minsalary)
SELECT CAST(REPLACE(SUBSTR(T1.salary, 4), ',', '') AS REAL) - CAST(REPLACE(SUBSTR(T2.minsalary, 4), ',', '') AS REAL) AS diff FROM employee AS T1  INNER JOIN position AS T2  ON T1.positionID = T2.positionID WHERE T1.lastname = 'Johnson' AND T1.firstname = 'James'