CREATE TABLE table_24970 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" TEXT, "U.S. viewers  ( millions ) " TEXT)

Who was the writer for the episode with 2.15 million u.s.viewers?
SELECT "Written by" FROM table_24970 WHERE "U.S. viewers (millions)" = '2.15'
SELECT "Written by" FROM "table_24970" WHERE "U.S. viewers (millions)" = '2.15'