Write SQL query to solve given problem: What was the average unit price of products shipped via United Package in 1997?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT AVG(T2.UnitPrice) FROM Orders AS T1 INNER JOIN `Order Details` AS T2 ON T1.OrderID = T2.OrderID INNER JOIN Shippers AS T3 ON T1.ShipVia = T3.ShipperID WHERE T1.OrderDate LIKE '1997%' AND T3.CompanyName = 'United Package'