Как используя понятие Класс и ООР дописать программу?

'Project name: Pennington Book Store
'Project purpose: Calculate and display the total amount a cuctomer owes 
 
'Created/revised by: Anna Pavlenko 04/25/2013
 
Option Explicit On
Option Strict On
Option Infer Off
 
 
Public Class Form1
 
 
    Private Sub exitButton_Click(sender As Object, e As System.EventArgs) Handles exitButton.Click
        Me.Close()
    End Sub
 
 
 
    Private Sub addToSaleButton_Click(sender As Object, e As System.EventArgs) Handles addToSaleButton.Click
        Dim quantity As Integer
        Dim price As Integer
        Dim totalDue As Integer = 0
 
        Integer.TryParse(quantityTextBox.Text, quantity)
        Integer.TryParse(priceTextBox.Text, price)
 
 
        totalDue = quantity * price
        totalDueLabel.Text = totalDue.ToString("N0")
        
 
    End Sub
 
 
    Private Sub newOrderButton_Click(sender As Object, e As System.EventArgs) Handles newOrderButton.Click
        quantityTextBox.Text = String.Empty
        priceTextBox.Text = String.Empty
    End Sub
End Class