user: Question: What is the average Area (in km²), when Markatal is less than 0?
Columns: ['Municipality', 'Population', 'Inhabitants per km²', 'Area (in km²)', 'Markatal', 'Island', 'Region']
Types: ['text', 'real', 'real', 'real', 'real', 'text', 'text']
Sample row: ['Tórshavnar kommuna', 19.339, 112.0, 173.0, 327.0, 'Streymoy', 'Tórshavn']
SQL:

assistant: SELECT AVG("Area (in km²)") FROM "Table" WHERE "Markatal" < 0.0;