user: ### NOW ANSWER:
Question: In what week was the Result L 15-13?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1.0, 'September 16, 1973', 'at Kansas City Chiefs', 'W 23-13', 62315.0]
SQL:

assistant: SELECT AVG("Week") FROM "Table" WHERE "Result" = 'L 15-13';