What's the average L/km combines when the L/100km Urban is 13.9, the mpg-UK combined is more than 28.5 and the mpg-UK extra urban is less than 38.7?
CREATE TABLE "see_also" (
  "manufacturer" text,
  "transmission" text,
  "engine_capacity" real,
  "fuel_type" text,
  "l_100km_urban_cold" real,
  "l_100km_extra_urban" real,
  "l_100km_combined" real,
  "mpg_uk_urban_cold" real,
  "mpg_uk_extra_urban" real,
  "mpg_uk_combined" real,
  "mpg_us_urban" real,
  "mpg_us_extra_urban" real,
  "mpg_us_combined" real,
  "co_2_g_km" real,
  "green_rating" text
);
SELECT AVG("l_100km_combined") FROM "see_also" WHERE "l_100km_urban_cold"=13.9 AND "mpg_uk_combined">28.5 AND "mpg_uk_extra_urban"<38.7;