Write SQL query to solve given problem: Of all the shipments made by United Package throughout the year 1996, what percentage correspond to the month of September?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(COUNT(CASE WHEN T1.ShippedDate LIKE '1996-09%' THEN 1 ELSE NULL END) AS REAL) * 100 / COUNT(T1.ShipVia) FROM Orders AS T1 INNER JOIN Shippers AS T2 ON T1.ShipVia = T2.ShipperID WHERE T2.CompanyName = 'United Package' AND T1.ShippedDate LIKE '1996%'