What is the average area for code 98030 with population over 312?
CREATE TABLE "list_of_municipalities_in_quebec" (
  "code" real,
  "type" text,
  "name" text,
  "area_km_2" real,
  "population" real,
  "regional_county_municipality" text,
  "region" real
);
SELECT AVG("area_km_2") FROM "list_of_municipalities_in_quebec" WHERE "code"=98030 AND "population">312;