Which Apollo Ltd customer's order number has the most expensive unit price, indicating the order date?
"Apollo Ltd" is the Customer Names; most expensive unit price refers to max(Unit Price)
SELECT T1.OrderNumber, T1.OrderDate FROM `Sales Orders` AS T1 INNER JOIN Customers AS T2 ON T2.CustomerID = T1._CustomerID WHERE T2.`Customer Names` = 'Apollo Ltd' ORDER BY T1.`Unit Price` DESC LIMIT 1