CREATE TABLE table_905 ("No. in series" TEXT, "No. in season" TEXT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Storyboarded by" TEXT, "Original air date" TEXT, "Production code" TEXT)

What's the production code of the episode with a series number 37b?
SELECT "Production code" FROM table_905 WHERE "No. in series" = '37b'
SELECT "Production code" FROM "table_905" WHERE "No. in series" = '37b'