user: Question: What was the population density in km2 for 2011 in the division where area in km2 was 684.37 in 2011? 
Columns: ['Administrative division', 'Area (km²) 2011**', 'Population 2001 Census (Adjusted)', 'Population 2011 Census (Adjusted)', 'Population density (/km² 2011)']
Types: ['text', 'text', 'real', 'real', 'text']
Sample row: ['Dhaka District', '1,463.6', 9036647.0, 12517361.0, '8,552.4']
SQL:

assistant: SELECT "Population density (/km² 2011)" FROM "Table" WHERE "Area (km²) 2011**" = '684.37';