Here's my code. By setting a max_circles constant, this program can be possibly extended to draw more circles with just a minor change on adding a calculation to determine each circle's radius which could be radius-=(radius/MAX_CIRCLES).

gistfile1.txt

import acm.graphics.*;
import acm.program.*;
import java.awt.*;

public class Target2 extends GraphicsProgram {
  private static final int MAX_CIRCLES=3;
	private static final int PIXELS_PER_INCH=72;
	public void run() {
		/* Set Initial Radius */
		double radius=1;
		drawTarget(radius);
		
	}
	private void drawTarget(double radius){
		radius*=PIXELS_PER_INCH;
		
		for(int i=0; i<MAX_CIRCLES; i++){
			
			double x=(getWidth()/2)-radius;
			double y=(getHeight()/2)-radius;
			GOval circle=new GOval(x, y, 2*radius, 2*radius);
			circle.setFilled(true);
			if (i%2==0){
			circle.setColor(Color.RED);
			}
			else{
				circle.setColor(Color.WHITE);	
			}
			add(circle);
			radius-=0.35*PIXELS_PER_INCH;
			
		
		
		}
	}