(start 800 600)
(define mid-y 300)
(define (backgroundColor color)
  (draw-solid-rect (make-posn 0 0) 800 600 color))
(backgroundColor 'yellow)
(define (centerCircle radius color)
  (draw-circle (make-posn mid-x mid-y) radius color))
(define (centerCircles radius increment color)
  (and (centerCircle radius color)
       (centerCircle (+ radius increment) color)
         (centerCircle (+ radius (* increment 2)) color)
         (centerCircle (+ radius (* increment 3)) color)))
(define (concentricCircles position radius increment color)
  (cond
    [(< radius 5) true]
    [else (and (draw-circle position radius color)
               (concentricCircles position (- radius increment)increment color))]))
    (concentricCircles (make-posn 400 300) 650 25 'blue)