CREATE TABLE table_27184 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "U.S. viewers  ( millions ) " TEXT)

What is the number in the series written by Steve Blackman and had a title of 'Worlds Apart'?
SELECT "No. in series" FROM table_27184 WHERE "Written by" = 'Steve Blackman' AND "Title" = 'Worlds Apart'
SELECT "No. in series" FROM "table_27184" WHERE "Title" = 'Worlds Apart' AND "Written by" = 'Steve Blackman'