What's the sum of the Area (KM 2) that's got a Population that's smaller than 90?
CREATE TABLE "main_places" (
  "place" text,
  "code" real,
  "area_km_2" real,
  "population" real,
  "most_spoken_language" text
);
SELECT COUNT("area_km_2") FROM "main_places" WHERE "population"<90;