CREATE TABLE table_3994 ("No. in series" FLOAT, "No. in season" FLOAT, "Title" TEXT, "Directed by" TEXT, "Written by" TEXT, "Original air date" TEXT, "Production code" FLOAT)

What is the production code that was written by matt robinson?
SELECT "Production code" FROM table_3994 WHERE "Written by" = 'Matt Robinson'
SELECT "Production code" FROM "table_3994" WHERE "Written by" = 'Matt Robinson'