[racket] why here a endless loop

I have this script :

(define (nettoloon h)
   ( - (brutoloon h) (belasting h)))

(define (belasting h)
   (cond
     [(< (brutoloon h) 240) (* 0 (brutoloon h))]
     [(and (< (brutoloon h) 480)  (> (brutoloon h) 240)) ( * 0.15 
(brutoloon h))]
     [else ( * 0.28 ( nettoloon h))]))

(define (brutoloon h)
   (* 12 h))

But it seems there a error in belasting.
When I do (belasting 239) I don't get a answer but a memory error 
problem. And I don't see why this happens.

Can anyone help me finding out what is wrong here ?

Regards,

Roelof Wobben