CREATE TABLE table_name_21 (area__km²_ INTEGER, population__2011_ VARCHAR(255), population_density VARCHAR(255))
What was the Area (km²) when the Population (2011) was 8574, and the Population density was larger than 381.4?
    
SQL: SELECT AVG(area__km²_) FROM table_name_21 WHERE population__2011_ = 8574 AND population_density > 381.4