CREATE TABLE table_21855 ("Episode" FLOAT, "Original title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original airdate" TEXT, "Duration" TEXT, "Viewership" TEXT)

Who was the director when the writer was John Sullivan?
SELECT "Directed by" FROM table_21855 WHERE "Written by" = 'John Sullivan'
SELECT "Directed by" FROM "table_21855" WHERE "Written by" = 'John Sullivan'