user: Question: What is the average number of laps with a DNF pos.?
Columns: ['Year', 'Team', 'Co-Drivers', 'Class', 'Laps', 'Pos.', 'Class Pos.']
Types: ['real', 'text', 'text', 'text', 'real', 'text', 'text']
Sample row: [2004.0, 'Rollcentre Racing', 'Martin Short Rob Barff', 'LMP1', 230.0, 'DNF', 'DNF']
SQL:

assistant: SELECT AVG("Laps") FROM "Table" WHERE "Pos." = 'DNF';