Can you please show which instructors are teaching those courses?
SELECT T2.emp_fname FROM CLASS AS T1 JOIN employee AS T2 ON T1.prof_num   =   T2.emp_num JOIN course AS T3 ON T1.crs_code   =   T3.crs_code
instructors are teaching refers to JOIN between class and employee tables; instructors' names refer to emp_fname; instructors are linked to courses through a common identifier between class and employee, and class and course tables.