What are the population densities of all communes with an are of 28.3 sq.km.?
CREATE TABLE "communes" (
  "commune" text,
  "area_km_2" text,
  "2002_population" real,
  "pop_density_km_2" text,
  "municipality_website" text
);
SELECT "pop_density_km_2" FROM "communes" WHERE "area_km_2"='28.3';