[plt-scheme] problem

I'm presently working through the exercises and have a question about
6.6.1;
it concerns making a structure definition for circle and i simply did
by
(define-struct circface (x y radius color))
and was able to draw the circle by:
(define (draw-a-circle a-circface)
  (draw-circle (make-posn (circface-x a-circface) (circface-y a-
circface))
                          (circface-radius a-circface) (circface-color
a-circface)))
What i tried to do initially was to define the circle structure by
imbedding
a posn structure within the definition but it just did not seem to
work. So
my question is: can you imbed a data structure within a new data
structure
definition? If so can i have a small hint?
oh example of circle structure used for drawing was defined by:
(define example1 (make-circface 100 100 50 'red))
thanks for any input
mike