What is the sum of people per km2 for the sandoy region with an area of 112.1?
CREATE TABLE "population_by_island" (
  "name" text,
  "area" real,
  "inhabitants" real,
  "people_per_km" real,
  "main_places" text,
  "regions" text
);
SELECT SUM("people_per_km") FROM "population_by_island" WHERE "regions"='sandoy' AND "area"=112.1;