how can i explain this without computer

[powerup]

class Child2 extends Parent{
private int a= 10;private int b= 20;
private void write (){
int c= a+ b;
System.out.println("The addition is"+ c);}
public static void main(String[] arg){
Child2 c=new Child2();
c.add();
c.write();
c.x=1000;
c.y=2000;
System.out.println("Now x is" + c.x);
System.out.println("Now y is" + c.y);
}
}
class Brother2 extends Parent{
public static void main(String[] arg){
Brother2 c=new Brother2();
c.add();
c.x=7000;
c.y=5700;
System.out.println("Now x is" + c.x);
System.out.println("Now y is" + c.y);
}
}
please gentelmen and ladies how can i explain the program's execution for searching the output for results regarding to mathmatics without using the computer
how can we tell our brain to extract output if it is division instead ("Now y is" + c.y);

[Waylander]

not very well apparently...