What is the average departure delay time of flights operated by American Airlines Inc.?
average departure delay time = DIVIDE(SUM(DEP_DELAY), COUNT(Code)); American Airlines Inc. refers to Description = 'American Airlines Inc.: AA';
SELECT AVG(T1.DEP_DELAY) FROM Airlines AS T1 INNER JOIN Airports AS T2 ON T2.Code = T1.ORIGIN INNER JOIN `Air Carriers` AS T3 ON T1.OP_CARRIER_AIRLINE_ID = T3.Code WHERE T3.Description = 'American Airlines Inc.: AA'