CREATE TABLE table_17981 ("Member countries" TEXT, "Population" FLOAT, "Area  ( km\\u00b2 ) " FLOAT, "GDP  ( billion US$ ) " TEXT, "GDP per capita  ( US$ ) " FLOAT)

What was the gdp of the country with a gdp per capita of $18048?
SELECT "GDP (billion US$)" FROM table_17981 WHERE "GDP per capita (US$)" = '18048'
SELECT "GDP (billion US$)" FROM "table_17981" WHERE "GDP per capita (US$)" = '18048'