CREATE TABLE table_74321 ("No. in series" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( million ) " TEXT)

How many million U.S. viewers saw the episode with production code 3X5710?
SELECT "U.S. viewers (million)" FROM table_74321 WHERE "Production code" = '3X5710'
SELECT "U.S. viewers (million)" FROM "table_74321" WHERE "Production code" = '3X5710'