8. Show the maximum and minimum TotalAmount in the INVOICE table. 9. Show the average of TotalAmount for Customer \#1 based on the INVOICE table. 10. Using the INVOICE_ITEM table, list the InvoiceNumber as well as the sum of Quantity for each and every invoice separately. (Hint: use GROUP BY for this and the following problems) 11. Using the INVOICE_ITEM table, count how many unique (i.e., distinctive) items are there for each and every invoice separately. 12. Using the INVOICE_ITEM table, list the InvoiceNumber as well as the sum of Quantity for each and every invoice separately, but only consider those items whose quantities are larger than 3 and whose UnitPrice is larger than $3.00 in your calculation. 13. Using the INVOICE_ITEM table, list the InvoiceNumber as well as the sum of Quantity, but only for those invoices whose sum of Quantity is larger than 15. Sort the results in descending order by an invoice's total Quantity