How do I solve this problem of a correlated subquery
Your query should be like:

SELECT FIRST_NAME, MIN_EMP_SALARY FROM
(
    SELECT  FIRST_NAME , (SELECT MIN(SALARY) 
                         FROM EMPLOYEES EMP
                         WHERE E.EMPLOYEE_ID = EMP.EMPLOYEE_ID
                         GROUP BY EMPLOYEE_ID) AS MIN_EMP_SALARY
    FROM  EMPLOYEES E
    GROUP BY FIRST_NAME , EMPLOYEE_ID
) OUTER_TABLE WHERE MIN_EMP_SALARY &gt;= 6000
ORDER BY MIN_EMP_SALARY DESC