Question: what episode does ken kaneki get his mask
[{'answer': '7', 'provenance': [{'wikipedia_id': '43329544', 'title': 'List of Tokyo Ghoul episodes', 'start_paragraph_id': 1, 'start_character': 200, 'end_paragraph_id': 1, 'end_character': 201, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]