user: Question: When was the first elected for district Missouri 7?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Missouri 2', 'Robert A. Young', 'Democratic', 1976.0, 'Re-elected', 'Robert A. Young (D) 56.4% Bob Chase (R) 43.6%']
SQL:

assistant: SELECT "First elected" FROM "Table" WHERE "District" = 'Missouri 7';