user: Question: What is the lowest Grid, when Laps is 21, when Manufacturer is Yamaha, and when Time is +18.802?
Columns: ['Rider', 'Manufacturer', 'Laps', 'Time', 'Grid']
Types: ['text', 'text', 'real', 'text', 'real']
Sample row: ['Valentino Rossi', 'Yamaha', 21.0, '43:06.007', 2.0]
SQL:

assistant: SELECT MIN("Grid") FROM "Table" WHERE "Laps" = 21.0 AND "Manufacturer" = 'Yamaha' AND "Time" = '+18.802';