user: Question: What is the average work number of Snowdon Ranger with the builder Vulcan Foundry?
Columns: ['Name', 'Builder', 'Type', 'Date', 'Works number']
Types: ['text', 'text', 'text', 'real', 'real']
Sample row: ['Snowdon Ranger', 'Vulcan Foundry', '0-6-4T', 1875.0, 739.0]
SQL:

assistant: SELECT AVG("Works number") FROM "Table" WHERE "Builder" = 'Vulcan Foundry' AND "Name" = 'Snowdon Ranger';