SCHEMA:
CREATE TABLE table_name_57 (population INTEGER, municipality VARCHAR, markatal VARCHAR, inhabitants_per_km² VARCHAR)
USER:
What is the sum of Population, when Markatal is greater than 48, when Inhabitants Per Km² is greater than 24, and when Municipality is Runavík?

QUERY:
SELECT SUM(population) FROM table_name_57 WHERE markatal > 48 AND inhabitants_per_km² > 24 AND municipality = "runavík"