Super keyword in Java

class Bill
{  private int bNo;
   protected double bAmt;

Bill(int x)
{  bNo=x;
}
public void showBill()
{   System.out.println(bAmt);
}
}
class MobilBill extends Bill
{  private double up;
   private int q;

MobilBill(int c,double a,int b)
{super(c);
 up=a;
 q=b;
}
public void getBill()
{  bAmt=up*q;
}
}
class A
{  public static void main(String arg[])
{  MobilBill m=new MobilBill(1,25,5);
   m.getBill();
   m.showBill();
}

}