Steve Johnson รองรับลูกค้าได้กี่ราย?
How many customers does Steve Johnson support?
employees_df = pd.DataFrame(columns=['id', 'first_name', 'last_name']); customers_df = pd.DataFrame(columns=['support_rep_id'])
customers_df[customers_df['support_rep_id'].isin(employees_df[(employees_df['first_name'] == 'Steve') & (employees_df['last_name'] == 'Johnson')]['id'])].count()