Finding subsets of length K in a list using low level Racket

Question

I believe I have read all of the posts on finding subsets of a given length. The implementation has been in Java, Python, C, etc.

I found the following code for Racket - Language level at Intermediate

(define (comb lst n)
  (cond 
    [(zero? n)'(())]
    [(empty? lst) '()]
    [else
         (append (map (lambda (x) (cons (first lst) x))
                      (comb (rest lst) (- n 1)))
                 (comb (rest lst) n))]
    )
)

It is elegant code, but I need to amend the above to only use beginner language. I am forbidden from using the length function or writing my own. I have written beginner code for generating the powerset. I have attempted to move the (map (lambda....)) into a helper function with the same template for map, but the results are not the same.

As I understand the recursion issue, I append the results of recursively cons'ing the first element with the rest of the list with n-1. I simultaneously send it to recursion with the first element not consed to the rest of the list with n.