user: Question: What is the average speed of rider Peter Williams?
Columns: ['Rank', 'Rider', 'Team', 'Speed', 'Time']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Malcolm Uphill', 'Triumph', '97.71mph', '1:55.51.4']
SQL:

assistant: SELECT AVG("Speed") FROM "Table" WHERE "Rider" = 'Peter Williams';