When was the Tennessee 3 district incumbent first elected? 
{'header': ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates'], 'page_title': 'United States House of Representatives elections, 1946', 'section_title': '', 'caption': '', 'rows': [['Tennessee 1', 'B. Carroll Reece', 'Republican', '1932', 'Retired Republican hold', 'Dayton E. Phillips (R) Unopposed'], ['Tennessee 3', 'Estes Kefauver', 'Democratic', '1939', 'Re-elected', 'Estes Kefauver (D) 90.8% George Bagwell (I) 9.2%'], ['Tennessee 4', 'Albert Gore, Sr.', 'Democratic', '1938', 'Re-elected', 'Albert Gore, Sr. (D) 67.5% H. E. McLean (R) 32.5%'], ['Tennessee 5', 'Harold Earthman', 'Democratic', '1944', 'Lost renomination Democratic hold', 'Joe L. Evins (D) Unopposed'], ['Tennessee 6', 'Percy Priest', 'Democratic', '1940', 'Re-elected', 'Percy Priest (D) 77.1% Will T. Perry (R) 22.9%'], ['Tennessee 7', 'W. Wirt Courtney', 'Democratic', '1939', 'Re-elected', 'W. Wirt Courtney (D) Unopposed'], ['Tennessee 8', 'Tom J. Murray', 'Democratic', '1942', 'Re-elected', 'Tom J. Murray (D) Unopposed'], ['Tennessee 9', 'Jere Cooper', 'Democratic', '1928', 'Re-elected', 'Jere Cooper (D) Unopposed']]}