0. #lang racket
1.  
2. (require 2htdp/image)
3. (define (pixels img)
4.     (if (image? img)
5.         (* (image-width img) (image-height img))
6.         (error "it's not a image")))
7. (define my-cir (circle 20 "solid" "purple"))
8. (define my-rec (rectangle 20 20 "solid" "black"0))
9. my-cir
10. my-rec
11. (pixels my-cir)
12. (pixels my-rec)

=>

rectangle: arity mismatch;

the expected number of arguments does not match the given

number

expected: 4

given: 5

my-rec: undefined;

cannot reference an identifier before its definition

in module: 'm

1600

my-rec: undefined;

cannot reference an identifier before its definition

in module: 'm