Here is one correct answer:
  public static void main ( String[] args )
  {
    Goods   toy ;
    Taxable tax = new Toy ( "Building Blocks", 1.49, 6 );
    toy = (Toy)tax;
    toy.display();
    System.out.println( "Tax: "+ ((Taxable)toy).calculateTax() );
  }
The first type cast must cast tax to a type 
Goods (or an ancestor).
The second must cast toy to Taxable or to
a class that implements Taxable.
Here is another possible answer:
  public static void main ( String[] args )
  {
    Goods   toy ;
    Taxable tax = new Toy ( "Building Blocks", 1.49, 6 );
    toy = (Goods)tax;
    toy.display();
    System.out.println( "Tax: "+ ((Toy)toy).calculateTax() );
  }
        Is this answer correct?