How many cards are there in the set 'World Championship Decks 2004' with the converted mana cost as '3'.
the set 'World Championship Decks 2004' refers to name = 'World Championship Decks 2004'
SELECT COUNT(id) FROM cards WHERE setCode IN ( SELECT code FROM sets WHERE name = 'World Championship Decks 2004' ) AND convertedManaCost = 3