[racket] Can't create circles

I'm learning how to use the Racket program, I'm still at the prologue
of the Second edition of how to design programs. When I type in:



(* (image-width )
   (image-height ))


or


(circle 10 "solid" "red")


or



(rectangle 30 20 "outline" "blue")



I get the error message:


image-width: this function is not defined
circle: this function is not defined
rectangle: this function is not defined


I don't know what to do,
Thanks in advance,
Geoff.