What year was the carriage type is 47' 6" 'birdcage' gallery coach built
CREATE TABLE "locomotives_and_rolling_stock" (
  "number" text,
  "tms_number" text,
  "builder" text,
  "year_built" real,
  "carriage_type" text
);
SELECT "year_built" FROM "locomotives_and_rolling_stock" WHERE "carriage_type"='47'' 6\" ''Birdcage'' gallery coach';