How big (in km2) is the voivodenship also known by the abbreviation KN?
CREATE TABLE "polish_voivodeships_and_separate_cities_" (
  "abbreviation" text,
  "voivodeship" text,
  "capital" text,
  "area_km_1998" text,
  "population_1980" text,
  "no_of_cities" real,
  "no_of_communes" real
);
SELECT "area_km_1998" FROM "polish_voivodeships_and_separate_cities_" WHERE "abbreviation"='kn';