MailPiece.cs

public abstract class MailPiece
{
    public abstract decimal Postage { get; set; }
    public abstract decimal Width { get; set; }
    public abstract decimal Height { get; set; }
    public abstract decimal Thickness { get; set; }

    public string GetStatistics(int zipCode)
    {
        return string.Format("Zip code is {0}, postage is {1} and height is {2}",
            zipCode, Postage, Height);
    }
}