[racket] printf: this function is not defined

I'm having trouble with the racket guide. First of all, I havent used it in
a little while, so I was surprised when I looked for the guide, and I think
it's new, and I can't find the old one.

That's not my main problem, though. I'm at the section that goes like this:

A function definition can include multiple expressions for the function’s
body. In that case, only the value of the last expression is returned when
the function is called. The other expressions are evaluated only for some
side-effect, such as printing.

Examples:
(define (bake flavor)
  (printf "pre-heating oven...\n")
  (string-append flavor " pie"))
> (bake "apple")
pre-heating oven...
"apple pie"

Here's everything I've entered so far.

(define (extract str)
  (substring str 4 7))


(extract "the boy out of the country")
(extract "the country out of the boy")

(define (bake flavor)
  (printf "preheating oven..\n")
  (string-append flavor " pie"))

(bake "apple")

and I get the error message

define: expected only one expression for the function body, but found 1
extra part

So I try taking out (string-append flavor " pie") and get a second error
message

printf: this function is not defined


I understand that define expects two sections after it (the name it defines
and the definition it enters when triggered) so in this case the
"string-append" would be the one extra. But I dont understand why the
"printf" thing doesn't work. Nor do I know what the "printf" function does,
as it's not explained in the guide.

I tried entering *just* what the guide said to enter, as in copy pasting it
in, but still get the same problems.

Any help? :(
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