Question: In the Northeast region, what is the average household income for each city located in the state with the highest number of stores?
SQL: SELECT AVG(T2.`Household Income`) FROM Regions AS T1 INNER JOIN `Store Locations` AS T2 ON T2.StateCode = T1.StateCode WHERE T1.Region = 'Northeast' GROUP BY T2.State ORDER BY COUNT(T2.StoreID) DESC LIMIT 1