Name the mccain % for dukes
{'header': ['County', 'McCain %', 'McCain Votes', 'Obama %', 'Obama Votes', 'Others %', 'Others Votes'], 'page_title': 'United States presidential election in Massachusetts, 2008', 'page_id': '', 'types': ['text', 'text', 'real', 'text', 'real', 'text', 'real'], 'id': '1-15929156-3', 'section_title': 'By county', 'caption': 'By county', 'rows': [['Barnstable', '42.1%', '55694', '56.1%', '74264', '1.8%', '2395'], ['Berkshire', '22.5%', '14876', '74.9%', '49558', '2.6%', '1696'], ['Bristol', '37.2%', '90531', '60.4%', '146861', '2.4%', '5728'], ['Dukes', '23.1%', '2442', '75.0%', '7913', '1.9%', '198'], ['Essex', '38.8%', '137129', '59.1%', '208976', '2.1%', '7357'], ['Franklin', '24.8%', '9545', '72.5%', '27919', '2.8%', '1065'], ['Hampden', '36.1%', '71350', '61.4%', '121454', '2.5%', '4916'], ['Hampshire', '25.9%', '20618', '71.5%', '56869', '2.6%', '2083'], ['Middlesex', '33.9%', '245766', '64.0%', '464484', '2.2%', '15781'], ['Nantucket', '30.8%', '1863', '67.3%', '4073', '1.9%', '116'], ['Norfolk', '39.7%', '136841', '58.2%', '200675', '2.1%', '7400'], ['Plymouth', '45.2%', '112904', '52.8%', '131817', '2.0%', '5096'], ['Suffolk', '21.2%', '57194', '76.9%', '207128', '1.8%', '4900']], 'name': 'table_15929156_3'}