user: ### NOW ANSWER:
Question: what is the area (km²) when the rank is south africa and the population (2011) is more than 51770561?
Columns: ['Rank', 'Province', 'Population (2011)', 'Area (km²)', 'Density (per km²)']
Types: ['text', 'text', 'real', 'real', 'real']
Sample row: ['1', 'Gauteng', 12272263.0, 18178.0, 675.1]
SQL:

assistant: SELECT AVG("Area (km²)") FROM "Table" WHERE "Rank" = 'south africa' AND "Population (2011)" > 51770561.0;