Question: how many dominoes are in a mexican train set
[{'answer': 'A double - twelve set', 'provenance': [{'wikipedia_id': '7727938', 'title': 'Mexican Train', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 22, 'bleu_score': 1.0, 'section': 'Section::::Equipment.\n'}]}, {'provenance': [{'wikipedia_id': '7727938', 'title': 'Mexican Train', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 233, 'bleu_score': 0.950578622812921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 544061329166198012}, 'section': 'Section::::Equipment.\n'}]}]