CREATE TABLE table_30936 ("Series #" FLOAT, "Production Code" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "United States Original Airdate" TEXT, "Canada Original Airdate" TEXT)

Who were the writers of the episodes directed by Greg Sullivan and which first aired on July 21, 2012?
SELECT "Written by" FROM table_30936 WHERE "Directed by" = 'Greg Sullivan' AND "United States Original Airdate" = 'July 21, 2012'
SELECT "Written by" FROM "table_30936" WHERE "Directed by" = 'Greg Sullivan' AND "United States Original Airdate" = 'July 21, 2012'