user: Question: What is the mean number of laps when time/retired was Spun off and the driver was Nick Heidfeld?
Columns: ['Driver', 'Constructor', 'Laps', 'Time/Retired', 'Grid']
Types: ['text', 'text', 'real', 'text', 'real']
Sample row: ['Michael Schumacher', 'Ferrari', 55.0, '1:47:34.801', 1.0]
SQL:

assistant: SELECT AVG("Laps") FROM "Table" WHERE "Time/Retired" = 'Spun off' AND "Driver" = 'Nick Heidfeld';