Find the first name of the professor who is teaching two courses with code CIS-220 and QM-261.
select t1.emp_fname from employee as t1 join class as t2 on t1.emp_num = t2.prof_num where crs_code = 'CIS-220' intersect select t1.emp_fname from employee as t1 join class as t2 on t1.emp_num = t2.prof_num where crs_code = 'QM-261'