user: ### NOW ANSWER:
Question: Which Week has a Result of W 20-13?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1.0, 'September 8, 1985', 'Kansas City Chiefs', 'L 47-27', 57760.0]
SQL:

assistant: SELECT AVG("Week") FROM "Table" WHERE "Result" = 'W 20-13';