How many basic or medium undergraduate courses are taught by a professor?
basic or medium undergraduate courses refers to courseLevel = 'Level_300'; professor refers to professor = 1
SELECT COUNT(*) FROM course AS T1 INNER JOIN taughtBy AS T2 ON T1.course_id = T2.course_id INNER JOIN person AS T3 ON T3.p_id = T2.p_id WHERE T1.courseLevel = 'Level_300' AND T3.professor = 1