Question: when does empire season 4 episode 18 air
[{'answer': 'May 23 , 2018', 'provenance': [{'wikipedia_id': '55191027', 'title': 'Empire (season 4)', 'start_paragraph_id': 1, 'start_character': 643, 'end_paragraph_id': 1, 'end_character': 656, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]