Question: how many episodes are in empire season 4
[{'answer': '18', 'provenance': [{'wikipedia_id': '46198833', 'title': 'List of Empire episodes', 'start_paragraph_id': 2, 'start_character': 54, 'end_paragraph_id': 2, 'end_character': 56, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]