What is the mean Year when the IWCR number was 5 and the Year withdrawn was bigger than 1926?
CREATE TABLE "locomotives_of_the_southern_railway" (
  "iwcr_no" text,
  "name" text,
  "wheel_arrangement" text,
  "sr_no" text,
  "year_made" real,
  "year_withdrawn" real
);
SELECT AVG("year_made") FROM "locomotives_of_the_southern_railway" WHERE "iwcr_no"='5' AND "year_withdrawn">1926;