title: Error: Does not implement interface member
body: <p>I'm new to c#, and I'm kinda struggling with implementing interfaces, gonna be very grateful if someone helps me with this, with an explanation. Thanks  </p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  namespace interfejsi
   interface Figura
  {
    String Plostina ();
    String Perimeter ();
  }
  }
   using System;
   using System.Collections.Generic;
   using System.Linq;
   using System.Text;
   namespace interfejsi
  {
   class Kvadar : Figura
  {
      int a,b,c;
      public  String Perimetar(int a, int b, int c)
      {
          return (a + b + c).ToString();
      }
      public String Plostina(int a, int b, int c)
      {
          return (a * b * c).ToString();
      }
  }
  </code></pre>
  
  <p>}</p>