user: Question: what is the size km² when the density hab/km is 8321?
Columns: ['Number', 'District', 'Size km²', 'Population', 'Density hab/km', 'Councilman', 'Party']
Types: ['real', 'text', 'real', 'real', 'real', 'text', 'text']
Sample row: [1.0, 'Ciutat Vella', 4.49, 111290.0, 24786.0, 'Carles Martí i Jufresa', 'CiU']
SQL:

assistant: SELECT "Size km²" FROM "Table" WHERE "Density hab/km" = 8321.0;