user: Question: What is the week with W 31-21 result?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1.0, 'September 2, 1979', 'at New Orleans Saints', 'W 40-34', 70940.0]
SQL:

assistant: SELECT "Week" FROM "Table" WHERE "Result" = 'W 31-21';