Hi still stuck with the ugly scheme

the problem this time is to get the median of three values (easy)

I did all these :

(define (med x y z) (car(cdr(x y z)))

and it was accepted but when testing it

(med 3 4 5)

I will get this error

Error: attempt to call a non-procedure (2 3 4)

and when entering letters inetead of number i got

(md x y z)

Error: undefined varia
       y
       (package user)

using somthin else than x y z i got

(md d l m)

Error: undefined variable
       d
       (package user)

so what is wronge ?!