user: Question: What was the average grid at the time Vanwall was constructor and there were 17 laps?
Columns: ['Driver', 'Constructor', 'Laps', 'Time/Retired', 'Grid']
Types: ['text', 'text', 'real', 'text', 'real']
Sample row: ['Tony Brooks', 'Vanwall', 70.0, '2:03:47.8', 2.0]
SQL:

assistant: SELECT AVG("Grid") FROM "Table" WHERE "Constructor" = 'Vanwall' AND "Laps" = 17.0;