[racket] cube-all

I need to write a function that takes a list and cubes the whole list, for instance, (cube-all '(3 4 2 5)) returns (27 64 8 125).

So far I have the code below, but it is not working out like I want it to. Any advice or suggestions?
(define cube-all
(lambda (ls)
(if (null? ls)
     ls
(cons(car ls)(cube-all (cdr ls))
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