The Completed Book Class

public class Book  extends Goods implements Taxable
{
  protected String author;

  public Book( String des, double pr, String auth)
  {
    super( des, pr );
    author  = auth ;
  }


  public String toString()
  {
    return super.toString() + " author: " + author ;
  }

  public double calculateTax()
  {
    return price * TAXRATE ;
  }
}