Postcard.cs

public class Postcard : MailPiece
{
    public override decimal Postage { get; set; }
    public override decimal Width { get; set; }
    public override decimal Height { get; set; }
    public override decimal Thickness { get; set; }

    public Postcard()
    {
        Postage = 0.33M;
        Width = 6.0M;
        Height = 4.25M;
        Thickness = 0.016M;
    }
}