Calculate the average of the total ordered quantity of products purchased whose shipping method was Cargo Transport 5.
shipping method was Cargo Transport 5 refers to Name = 'Cargo Transport 5'; average = DIVIDE(SUM(OrderQty where Name = 'Cargo Transport 5'), COUNT(ShipMethodID))
SELECT CAST(SUM(IIF(T1.ShipMethodID = 5, T3.OrderQty, 0)) AS REAL) / COUNT(T3.ProductID) FROM ShipMethod AS T1 INNER JOIN PurchaseOrderHeader AS T2 ON T1.ShipMethodID = T2.ShipMethodID INNER JOIN PurchaseOrderDetail AS T3 ON T2.PurchaseOrderID = T3.PurchaseOrderID