user: Question: How many districts had William F. Norrell as the incumbent?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Arkansas 1', 'Ezekiel C. Gathings', 'Democratic', 1938.0, 'Re-elected', 'Ezekiel C. Gathings (D) Unopposed']
SQL:

assistant: SELECT COUNT("District") FROM "Table" WHERE "Incumbent" = 'William F. Norrell';