Converted relational model will comtain two tables :
1. Professor(Pid.........(other attributes), Cid) // Assuming column name for example, Pid->Primary Key, Cid- Foreign Key
2. Course(Cid.......(other attributes) // Cid ->Primary Key
Now as Cid is a foreign key in Professors table, tuples of cid in course table will be a subset of tuples of cid in professors table.
Hence maximum number of tuples is tuples in Professors table. Correct me if I'm wrong.