CREATE TABLE table_42838 ("Name" CLOB, "Seat" CLOB, "Population  ( 2011 ) " FLOAT, "Area  ( km 2  ) " FLOAT, "Density  ( inhabitants/km 2  ) " FLOAT)

For Stellenbosch, which has a population larger than 155,733, what is the average area?
SELECT AVG("Area (km 2 )") FROM table_42838 WHERE "Name" = 'stellenbosch' AND "Population (2011)" > '155,733'
SELECT AVG("Area (km 2 )") FROM "table_42838" WHERE "Name" = 'stellenbosch' AND "Population (2011)" > '155,733'