Question: what is the seating capacity of wembley arena
[{'answer': '12,500', 'provenance': [{'wikipedia_id': '596136', 'title': 'Wembley Arena', 'start_paragraph_id': 1, 'start_character': 177, 'end_paragraph_id': 1, 'end_character': 183, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]