CREATE TABLE table_name_57 (works_number NUMBER, builder VARCHAR2, name VARCHAR2)

What is the average work number of Snowdon Ranger with the builder Vulcan Foundry?
SELECT AVG(works_number) FROM table_name_57 WHERE builder = "vulcan foundry" AND name = "snowdon ranger"
SELECT AVG("works_number") FROM "table_name_57" WHERE "builder" = "vulcan foundry" AND "name" = "snowdon ranger"