Create a simple application that serves as a simple cash register for a retail store. use the Inventory class you created in Programming Challenge 7 to store data about the items in the store's inventory. When the application starts up, it should load the entire store's inventory from a file into a collection of Inventory objects.

When a purchase is made, the cashier should select an item from the a list box. (If an item's OnHand property is set to zero, the item should not be available in the list box.) The item's description, retail price, and number of units on hand should be displayed on the form when selected. The cashier should enter the quantity being purchased, and the application should display the sales tax and total of the sale. (The quantity purchased cannot exceed the number of units on hand.) The quantity being purchased should be subtracted from the item's OnHand property. When the application ends, the contents of the collection should be saved to the file.