What's the arable land for the population of 20,090,437?
CREATE TABLE "ranking" (
  "country" text,
  "population_july_2005_est" real,
  "land_area_km" real,
  "pct_of_arable_land_2005_est" text,
  "arable_land_km" real,
  "population_density_pop_per_km" real
);
SELECT MAX("arable_land_km") FROM "ranking" WHERE "population_july_2005_est"='20,090,437';