When 2/1939 is the withdrawn when was it built?
CREATE TABLE "numbers_and_names" (
  "hr_no" text,
  "hr_name" text,
  "cr_no" real,
  "lms_no" real,
  "built" text,
  "works" text,
  "withdrawn" text
);
SELECT "built" FROM "numbers_and_names" WHERE "withdrawn"='2/1939';