Write SQL query to solve given problem: How many flights on average does American Airlines Inc. operate every day in August, 2018?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST( SUM(CASE WHEN T2.FL_DATE LIKE '2018/8%' THEN 1 ELSE 0 END) AS REAL) / 31 FROM Airports AS T1 INNER JOIN Airlines AS T2 ON T1.Code = T2.ORIGIN INNER JOIN `Air Carriers` AS T3 ON T2.OP_CARRIER_AIRLINE_ID = T3.Code WHERE T3.Description = 'American Airlines Inc.: AA'