SCHEMA:
CREATE TABLE table_name_21 (area__km²_ INTEGER, population__2011_ VARCHAR, population_density VARCHAR)
USER:
What was the Area (km²) when the Population (2011) was 8574, and the Population density was larger than 381.4?

QUERY:
SELECT AVG(area__km²_) FROM table_name_21 WHERE population__2011_ = 8574 AND population_density > 381.4