Lagenmodel-oef5-Winform

Form1.cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace OefeninfenLagenForms
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Berekenknop_Click(object sender, EventArgs e)
        {
            Business b1 = new Business();

            MessageBox.Show(Convert.ToString(b1.berekenTeBetalen(Convert.ToDouble(txtBedraginv.Text))));

        }
    }
}

Business.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace OefeninfenLagenForms
{
    class Business
    {
        private double bedrag;
        public double Bedrag
        {
            get { return bedrag; }
            set { bedrag = value; }
        }
        public double berekenTeBetalen(double pbedrag)
        {
            double korting = 0.0;
            if (pbedrag > 0)
            {
                if (pbedrag < 50)
                {
                    korting = 0.025;
                }
                else if (pbedrag < 100)
                {
                    korting = 0.05;
                }
                else if (pbedrag <200)
                {
                    korting = 0.10;

                }
                else
                {
                    korting = 0.20;
                }
                return pbedrag - (pbedrag * korting );
            }
            return 0;
        }
    }
}