Answer:

interface Taxable
{
  final double taxRate = 0.06 ;
  double calculateTax() ;
}

Adding another Class

Since taxRate is a constant, it must be set to a value, here, 6 percent. Here is a partial definition of Toy. Recall that it:

Has a parent, Goods.
Adds a variable, minimumAge.
Is taxable.

class Toy extends Goods  
{
  int minimumAge;

  Toy( String des, double pr, int min)
  {
    super( des, pr );
    minimumAge  = min ;
  }

  void display()
  {
    super.display() ;
    System.out.println( "minimum age: " + minimumAge );
  }

  public double   // implementing the interface
  {
    return price *  ;
  }
}

QUESTION 11: