CREATE TABLE market (Number_cities INTEGER, Market_ID VARCHAR(255)); CREATE TABLE film_market_estimation (Market_ID VARCHAR(255), Low_Estimate INTEGER)
What is the average number of cities of markets with low film market estimate bigger than 10000?
    
SQL: 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