Write SQL query to solve given problem: List the marital status of customers within the age of 40 to 60 that has the highest income among the group.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T1.MARITAL_STATUS FROM Customers AS T1 INNER JOIN Demog AS T2 ON T1.GEOID = T2.GEOID WHERE T1.age >= 40 AND T1.age <= 60 ORDER BY T2.INCOME_K DESC LIMIT 1