CREATE TABLE table_21851 ("Episode" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original airdate" TEXT, "Duration" TEXT, "Viewership" TEXT)

How many people wrote the episode that had 6.34 million viewers?
SELECT COUNT("Written by") FROM table_21851 WHERE "Viewership" = '6.34 million'
SELECT COUNT("Written by") FROM "table_21851" WHERE "Viewership" = '6.34 million'