What Class has a Quantity made of 5?
CREATE TABLE "belfast_and_northern_counties_railway_18" (
  "class" text,
  "type" text,
  "fleet_numbers" text,
  "quantity_made" real,
  "manufacturer" text,
  "date_made" text,
  "date_withdrawn" text
);
SELECT "class" FROM "belfast_and_northern_counties_railway_18" WHERE "quantity_made"=5;