user: Question: What is the density of the common with an area of 20.4 km^2?
Columns: ['Rank', 'Common of', 'Population', 'Area (km 2 )', 'Density (inhabitants/km 2 )', 'Altitude (mslm)']
Types: ['text', 'text', 'real', 'text', 'text', 'real']
Sample row: ['1st', 'Torino', 907563.0, '130.7', '6943.9', 239.0]
SQL:

assistant: SELECT "Density (inhabitants/km 2 )" FROM "Table" WHERE "Area (km 2 )" = '20.4';