new file mode 100644
--- /dev/null
+++ b/Sales/Invoice.cs
@@ -0,0 +1,83 @@
+/**
+ * Invoice.cs
+ * 
+ * @author       Markus Bröker<broeker.markus@googlemail.com>
+ * @copyright    Copyright(C) 2017 4Customers UG
+ * 
+ */
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+using static Sales.Payment;
+
+namespace Sales
+{
+    delegate double InvoiceDelegate();
+
+    class Invoice
+    {
+        private double value = 0;
+        private PaymentType till;
+
+        public Invoice(double value, PaymentType till)
+        {
+            this.value = value;
+            this.till = till;
+
+            InvoiceDelegate invoiceDelegateReference = this.Rabatt;
+            invoiceDelegateReference += this.AddTax;
+            invoiceDelegateReference += this.Skonto;
+
+            invoiceDelegateReference();
+        }
+
+        public double getFinalResult()
+        {            
+            return value;
+        }
+
+        //Rabatt auf den Netto Preis
+        private double Rabatt()
+        {
+            if (value > 1000.0)
+            {
+                value *= 0.75;
+            }
+            else if (value > 500.0)
+            {
+                value *= 0.85;
+            }
+
+            return value;
+        }
+
+        // Steuern auf den rabattierten Nettopreis
+        private double AddTax()
+        {
+            value *= 1.19;
+            return value;
+        }
+
+        // Skonto immer zum Schluss
+        private double Skonto()
+        {
+            switch (till)
+            {
+                case PaymentType.NOW:
+                    value *= 0.97;
+                    break;
+                case PaymentType.WEEK:
+                    value *= 0.98;
+                    break;
+                case PaymentType.MONTH:
+                    value *= 0.99;
+                    break;
+            }
+
+            return value;
+        }
+    }
+}