16. Create a query to produce the total purchase per invoice, generating the results shown below, sorted by invoice number. The invoice total is the sum of the product purchases in the LINE that corresponds to the INVOICE. 17. Use a query to show the invoices and invoice totals in the table below. Sort the results by customer code and then by invoice number. 18. Write a query to produce the number of invoices and the total purchase amounts by customer, using the output shown in the table as your guide. Note the results are sorted by customer code. (Compare this summary to the results shown in Problem 17.) 21. Provide a summary of customer balance characteristics for customers who made purchases. Include the minimum balance, maximum balance, and average balance, as shown. 25. Create a query that summarizes the value of products currently in inventory. Note that the value of each product is a result of multiplying the units currently in inventory by the unit price. Sort the results in descending order by subtotal, as shown