Question: how many planes are in the delta fleet
[{'answer': '855'}, {'provenance': [{'wikipedia_id': '19994775', 'title': 'Delta Air Lines fleet', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 631, 'bleu_score': 0.615735372204958, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4805118995154224973}, 'section': 'Section::::Abstract.'}]}]