What is the highest Markatal, when Municipality is Leirvík, and when Inhabitants Per Km² is greater than 79?
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 MAX("markatal") FROM "local_government_in_the_faroe_islands" WHERE "municipality"='leirvík' AND "inhabitants_per_km">79;