How many polls show a result where democrat Christine Gregoire was polling at 50% and had a lead margin of 2?
{'header': ['Source', 'Dates administered', 'Democrat: Christine Gregoire', 'Republican: Dino Rossi', 'Lead Margin'], 'page_title': 'Opinion polling for the United States gubernatorial elections, 2008', 'page_id': '', 'types': ['text', 'text', 'text', 'text', 'text'], 'id': '1-17538810-7', 'section_title': '', 'caption': '', 'rows': [['Survey USA', 'November 2, 2008', '52%', '46%', '6'], ['Survey USA', 'October 27, 2008', '50%', '48%', '2'], ['Rasmussen Reports', 'October 22, 2008', '50%', '48%', '2'], ['Survey USA', 'October 13, 2008', '48%', '47%', '1'], ['Rasmussen Reports', 'October 2, 2008', '48%', '48%', '0'], ['Survey USA', 'September 21–22, 2008', '50%', '48%', '2'], ['Strategic Vision', 'September 14–16, 2008', '46%', '48%', '2'], ['Rasmussen Reports', 'September 10, 2008', '46%', '52%', '6'], ['Elway Poll', 'September 6–8, 2008', '48%', '44%', '4'], ['Survey USA', 'September 5–7, 2008', '47%', '48%', '1'], ['Survey USA', 'August 11–12, 2008', '50%', '48%', '2'], ['Rasmussen Reports', 'August 6, 2008', '50%', '46%', '4'], ['Elway Poll', 'July 27–31, 2008', '52%', '36%', '16'], ['Strategic Vision', 'July 25–27, 2008', '47%', '45%', '2'], ['Survey USA', 'July 13–15, 2008', '49%', '46%', '3'], ['Moore Information', 'July 9–10, 2008', '45%', '45%', '0'], ['Rasmussen Reports', 'July 9, 2008', '52%', '44%', '6'], ['Elway Poll', 'June 18–22, 2008', '47%', '39%', '8'], ['Rasmussen Reports', 'June 9, 2008', '50%', '43%', '7'], ['SurveyUSA', 'June 7–9, 2008', '50%', '47%', '3'], ['Rasmussen Reports', 'May 12, 2008', '52%', '41%', '11'], ['SurveyUSA', 'April 7, 2008', '48%', '47%', '1'], ['Rasmussen Reports', 'April 2, 2008', '47%', '46%', '1'], ['Rasmussen Reports', 'February 28, 2008', '46%', '47%', '1'], ['University of Washington', 'February 7–18, 2008', '53.7%', '42.1%', '11.6'], ['Strategic Vision', 'October 5–7, 2007', '47%', '45%', '2']], 'name': 'table_17538810_7'}