Using C#, Create a class called Invoice that a hardware store might use to represent an invoice for an item sold at the store. An Invoice should include four pieces of information as instance variables - a part number (type string), a part description (type string), a quantity of the item being purchased (type int) and a price per item (decimal). Your class should have a constructor that initializes the four variables. Provide a method named GetInvoiceAmount that calculates the invoice amount (i.e., multiplies the quantity by the price per item), then returns the amount as a decimal value. Write a class named InvoiceTest that demonstrates class Invoices capabilities. That is, creating an instance of Invoice by calling its constructor and then call its method GetInvoiceAmount. These two classes are in the same namespace