What is the area of the city with a density of 955.6?
CREATE TABLE "population_by_district" (
  "city_district" text,
  "area_km" text,
  "population_2007_census_hab" text,
  "housing_2007" text,
  "density_hab_km" text,
  "elevation_msl" text
);
SELECT "area_km" FROM "population_by_district" WHERE "density_hab_km"='955.6';