CREATE TABLE table_28724 ("No." FLOAT, "#" FLOAT, "Title" CLOB, "Directed by" CLOB, "Written by" CLOB, "U.S. air date" CLOB, "Production code" CLOB, "U.S. viewers  ( million ) " CLOB)

On which date did episode # 18 air in the U.S.?
SELECT "U.S. air date" FROM table_28724 WHERE "#" = '18'
SELECT "U.S. air date" FROM "table_28724" WHERE "#" = '18'