Königsbrück (Upper Sorbian: "Kinspork") is a town in the Bautzen district, in the Free State of Saxony, Germany.
 It is situated 14 km west of Kamenz, and 27 km northeast of the Saxon capital Dresden.
 Königsbrück is known as the western gate of the historic Upper Lusatia region.
Upper Lusatia (German: "Oberlausitz" ; Upper Sorbian: "Hornja Łužica" ; Lower Sorbian: "Górna Łužyca" ; Polish: "Łużyce Górne" or "Milsko"; ) is a historical region in Germany and Poland.
 Along with Lower Lusatia to the north, it makes up the region of Lusatia, named after the Slavic "Lusici" tribe.
 Both Lusatias are home to the West Slavic minority group of the Sorbs.
Bad Muskau (] ; formerly "Muskau", Upper Sorbian: "Mužakow" , Polish: "Mużaków" ) is a spa town in the historic Upper Lusatia region in Germany at the border with Poland.
 It is part of the Görlitz district in the State of Saxony.
Lausche (Czech: "Luž" ), is, at 793 m , the highest peak of the Lusatian Mountains and the highest mountain in the German part of the Upper Lusatia region.
 The conical mountain is part of the Zittau Mountains range, situated on the border of the German state of Saxony with the Bohemian region of the Czech Republic.
Lower Lusatia (German: "Niederlausitz" , Lower Sorbian: "Dolna Łužyca" , Upper Sorbian: "Delnja Łužica" , Polish: "Łużyce Dolne" , ) is a historical region in Central Europe, stretching from the southeast of the German state of Brandenburg to the southwest of Lubusz Voivodeship in Poland.
 Like adjacent Upper Lusatia in the south, Lower Lusatia is a settlement area of the West Slavic Sorbs whose endangered Lower Sorbian language is related to Upper Sorbian and Polish.
Silesia ( ; Polish: "Śląsk" ; Czech: "Slezsko" ; German:    ] ; Silesian German: "Schläsing"; Silesian: "Ślůnsk" [ɕlonsk] ; Lower Sorbian: "Šlazyńska" ; Upper Sorbian: "Šleska" ; Latin: "Silesia" ) is a region of Central Europe located mostly in Poland, with small parts in the Czech Republic and Germany.
 Its area is about 40,000 km2 , and its population about 8,000,000.
 Silesia is located along the Oder River.
 It consists of Lower Silesia and Upper Silesia.
Ruszów (German: "Rauscha" ) is a village in the administrative district of Gmina Węgliniec, within Zgorzelec County, Lower Silesian Voivodeship, in south-western Poland.
 Ruszów is within the historic Upper Lusatia, homeland of Lusatian Sorbs.
 It lies approximately 13 km north of Węgliniec, 31 km north-east of Zgorzelec, and 133 km west of the regional capital Wrocław.
Złotniki Lubańskie (German: "Goldentraum" ) is a village in the administrative district of Gmina Leśna, within Lubań County, Lower Silesian Voivodeship, in south-western Poland.
 Situated on the left bank of the Kwisa river, the settlement was formerly part of the historic Upper Lusatia region at the border with Silesia.
Muskau Park (German: "Muskauer Park" , officially: "Fürst-Pückler-Park Bad Muskau"; Polish: "Park Mużakowski" ) is a landscape park in the Upper Lusatia region of Germany and Poland.
 It is the largest and one of the most famous English gardens in Central Europe, stretching along both sides of the German–Polish border on the Lusatian Neisse.
 The park was laid out from 1815 onwards at the behest of Prince Hermann von Pückler-Muskau (1785–1871), centered on his Schloss Muskau residence.
The King Frederick Augustus Tower (German: "König-Friedrich-August-Turm" ) is the only preserved observation tower of cast iron in Europe and perhaps the oldest tower built of iron.
 It is located on the "Löbauer Berg" at Löbau in Saxony, offering a panoramic view of the Zittau Hills and the Upper Lusatia region.
 The tower was built in 1854 by the Löbau citizens and named after King Frederick Augustus II of Saxony.

Question: What is the area of this region of Central Europe located mostly in Poland, in which Złotniki Lubańskie was formerly part of the historic Upper Lusatia region at its border?
Answer: 40,000 km2