Question: how many episodes are in series 4 of shetland
[{'answer': '6', 'provenance': [{'wikipedia_id': '38859978', 'title': 'Shetland (TV series)', 'start_paragraph_id': 3, 'start_character': 280, 'end_paragraph_id': 3, 'end_character': 281, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]