Which Livery has a Description of 20t tanker, with a date later than 1941?
CREATE TABLE "tanker_wagons" (
  "number_name" text,
  "description" text,
  "current_status" text,
  "livery" text,
  "date" real
);
SELECT "livery" FROM "tanker_wagons" WHERE "description"='20t tanker' AND "date">1941;