add overriding

TicketSystem/Tickets/Adult.cs

@@ -1,17 +0,0 @@
-namespace TicketSystem.Tickets
-{
-    public class Adult: Ticket
-    {
-        public int price { get; }
-
-        public Adult()
-        {
-            price = 20;
-        }
-
-        public int PriceWithReduction()
-        {
-            return price - price/100*20;
-        }
-    }
-}

TicketSystem/Tickets/Ticket.cs

@@ -7,9 +7,17 @@
         Adult
     }
 
-    public interface Ticket
+    public class Ticket
     {
-        int price { get; }
-        int PriceWithReduction();
+        public int price { get; }
+        public Ticket()
+        {
+            price = 20;
+        }
+
+        public int PriceWithReduction()
+        {
+            return price - price/100*20;
+        }
     }
 }