[racket] structures question

Hello,

Im trying to make a programm which use structures and calculates the 
distance between a point and another point.
The first point has coordinates (0,0).

So I made this :

;; Posn -> Number.
;; A programm for calculating the distance is Manhatten
(check-expect ( manhatten (make-posn 7 3 ) 10))
(check-expect ( manhatten (make-posn 1 1 ) 2))

(define (manhatten pos-manhatten)
  ( + (pos-y posmanhetten) (pos-x manhetten)))

I get this message :

check-expect: expects 2 arguments, but found only 1

But there is only 1 argument the structure pos-manhatten.

Roelof