What's the approximate number of HUs when there are more than 2 digits, and 6 levels?
CREATE TABLE "united_states" (
  "name" text,
  "level" real,
  "digits" real,
  "average_size_square_miles" text,
  "number_of_h_us_approximate" real,
  "example_name" text,
  "example_code_huc" real
);
SELECT COUNT("number_of_h_us_approximate") FROM "united_states" WHERE "digits">2 AND "level"=6;