Trying to understand Puzzle4..Head First

[qsas sasa]

Hi!! I'm trying to understand the sharpen your pencil Class Puzzle4 from head first java.. But the math and the logic is confusing me... I hope someone can give me some explanation before I move on in the book... The output of the code should be Result 543345

  public class Puzzle4 {
	public static void main (String[] args){
		
		Puzzle4b[] obs = new Puzzle4b[6];
		
		int y = 1;
		int x = 0;
		int result = 0;
		while (x < 6){
			
			obs[x] = new Puzzle4b();
			obs[x].ivar = y;
			System.out.println("obs[x] = " + obs[x].ivar);
			y = y * 10;
			System.out.println(" Y = " + y);
			x = x + 1;
			System.out.println(" x = " + x);
			
		}
		x = 6;
		System.out.println(" x = " + x);
		while (x > 0){
			x = x - 1;
			System.out.println(" x = " + x);
			System.out.println("obs[x].doStuff(x) = " + obs[x].doStuff(x));
			result = result + obs[x].doStuff(x);
		}
		System.out.println("Result " + result);
	}

ivar is an instance and the value of it is unique to every object is that right?? The logic of the method is confusing me. I understand that x is the argument to

public int doStuff(int factor)/code]... and can someone please explain [code=java]return ivar * ( 5 - factor );

class Puzzle4b {
	int ivar;
	
	
	public int doStuff(int factor){
		if (ivar > 100){
			return ivar * factor;
		}
		else{
			return ivar * ( 5 - factor );
		}
	}
	
	
}