CREATE TABLE table_18043 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" FLOAT, "U.S. viewers  ( millions ) " TEXT)

How many episodes originally aired on April 29, 2008?
SELECT COUNT("No. in series") FROM table_18043 WHERE "Original air date" = 'April 29, 2008'
SELECT COUNT("No. in series") FROM "table_18043" WHERE "Original air date" = 'April 29, 2008'