What is the per-capita GDP for the country with an overall GDP of 156.640?
CREATE TABLE "1995_enlargement" (
  "member_countries" text,
  "population" text,
  "area_km" text,
  "gdp_billion_us" text,
  "gdp_per_capita_us" text
);
SELECT "gdp_per_capita_us" FROM "1995_enlargement" WHERE "gdp_billion_us"='156.640';