What is the sum of Markatal, when Inhabitants Per Km² is less than 13, and when Area (in Km²) is 27?
CREATE TABLE "local_government_in_the_faroe_islands" (
  "municipality" text,
  "population" real,
  "inhabitants_per_km" real,
  "area_in_km" real,
  "markatal" real,
  "island" text,
  "region" text
);
SELECT SUM("markatal") FROM "local_government_in_the_faroe_islands" WHERE "inhabitants_per_km"<13 AND "area_in_km"=27;