And what are their student numbers?
SELECT T2.STU_NUM FROM CLASS AS T1 JOIN enroll AS T2 ON T1.class_code   =   T2.class_code JOIN course AS T3 ON T1.crs_code   =   T3.crs_code JOIN department AS T4 ON T3.dept_code   =   T4.dept_code WHERE T4.dept_name   =   'Accounting'
their refers to students; student numbers refers to STU_NUM; students in the Accounting department refers to filtering by dept_name = 'Accounting';