/* TEMPLATE for the Rect class:
  int distTo0() {
    ... this.nw ...
        ... this.nw.x ...
        ... this.nw.y ...
    ... this.width ...
    ... this.height ... }  */

 /* TEMPLATE for the Dot class:
  int distTo0() {
    ... this.location ...
        ... this.location.x ...
        ... this.location.y ... }  */

5. Program:

Again, we have three different methods, one for each class.

  // PROGRAM for the class Circle: 
  int distTo0() {
    return this.center.distTo0(); }  

  // PROGRAM for the class Rect: 
  int distTo0() {
    return this.nw.distTo0(); }  

  // PROGRAM for the class Dot: 
  int distTo0() {
    return this.location.distTo0(); }  

6. Tests:

  c1.distTo0()  == 30
  c2.distTo0()  == 60
  r1.distTo0()  == 30
  r2.distTo0()  == 60
  d1.distTo0()  == 30
  d2.distTo0()  == 60