How many city/municipalties have an area (km2) of 506.64?
CREATE TABLE "bukidnon" (
  "city_municipality" text,
  "date_of_creation" text,
  "area_km_2" text,
  "population_2010" real,
  "income_classification_dof" text
);
SELECT COUNT("city_municipality") FROM "bukidnon" WHERE "area_km_2"='506.64';