CREATE TABLE table_name_85 (capacity NUMBER, city VARCHAR2, stadium VARCHAR2)

Which Capacity has a City of london, and a Stadium of queen's club?
SELECT AVG(capacity) FROM table_name_85 WHERE city = "london" AND stadium = "queen's club"
SELECT AVG("capacity") FROM "table_name_85" WHERE "city" = "london" AND "queen's club" = "stadium"