How many 2010 estimations have been done in the city of Cremona?
CREATE TABLE "references" (
  "num" real,
  "city" text,
  "1981_census" real,
  "1991_census" real,
  "2001_census" real,
  "2010_est" real,
  "region" text
);
SELECT COUNT("2010_est") FROM "references" WHERE "city"='Cremona';