CREATE TABLE table_28242 ("No. in series" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( million ) " TEXT)

Which prod code was series 11?
SELECT "Production code" FROM table_28242 WHERE "No. in series" = '11'
SELECT "Production code" FROM "table_28242" WHERE "No. in series" = '11'