Error - Create A Class Called Invoice - Hardware Store Use To Represent An Invoice For An Item Sold At Store

"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 Integer) and a price per item (Type Integer). Your class should have a constructor that initialize for each of the four instance variables. Provide a property for each instance variable. If the quantity is not positive it should be set to zero. If the price per item is not positive it should be set to zero."

I attached the code I have. obj is underlined and says "Argument not specified for parameter 'Invoice4' of the 'Public Sub New (Invoice1 As Object, Invoice2 As Object, Invoice3 As Object, Invoice4 As Object)' and so the program won't run. What am I doing wrong?

Public Class Form1

Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
Dim obj1 As New Invoice(Val(TextBox1.Text))
TextBox1.Text &= obj1.Invoice1 & vbNewLine
TextBox1.Text &= obj1.Invoice2 & vbNewLine
TextBox1.Text &= obj1.Invoice3 & vbNewLine
TextBox1.Text &= obj1.Invoice4 & vbNewLine

[CODE]...