What class has 4-4-0 wheels and was less than number 40 built?
CREATE TABLE "1923_1937" (
  "class" text,
  "wheels" text,
  "date" text,
  "builder" text,
  "no_built" real
);
SELECT "class" FROM "1923_1937" WHERE "wheels"='4-4-0' AND "no_built"<40;