Translate the following question to SQL: Give the average number of cities within markets that had a low market estimation larger than 10000?

Schema: CREATE TABLE film (
    Film_ID INT   PRIMARY KEY,
    Title TEXT,
    Studio TEXT,
    Director TEXT,
    Gross_in_dollar INT,
    UNIQUE (Film_ID)
);

CREATE TABLE market (
    Market_ID INT   PRIMARY KEY,
    Country TEXT,
    Number_cities INT,
    UNIQUE (Market_ID)
);

CREATE TABLE film_market_estimation (
    Estimation_ID INT   PRIMARY KEY,
    Low_Estimate REAL,
    High_Estimate REAL,
    Film_ID INT,
    Type TEXT,
    Market_ID INT,
    Year INT,
    UNIQUE (Estimation_ID),
    FOREIGN KEY (Market_ID) REFERENCES market(Market_ID),
    FOREIGN KEY (Film_ID) REFERENCES film(Film_ID)
);
user
SELECT avg(T2.Number_cities) FROM film_market_estimation AS T1 JOIN market AS T2 ON T1.Market_ID  =  T2.Market_ID WHERE T1.Low_Estimate  >  10000
assistant