[racket] what's the best way to make auxilery functions here.

Hello,

I have this function :

; Vzoo -> Vzoo
; function which alters the happiness and x-coordinate based on the 
ticks of the computer.
(check-expect (tock (make-VZoo (make-VCat 500 5 "rechts") (make-VCham 
450 5 "rechts"))) (make-VZoo (make-VCat 503 4.9 "rechts")(make-VCham 453 
4.9 "rechts")))
(check-expect (tock (make-VZoo (make-VCat 500 5 "rechts") (make-VCham 
1032 5 "rechts"))) (make-VZoo (make-VCat 503 4.9 "rechts")(make-VCham 
1032 4.9 "links")))
(check-expect (tock (make-VZoo (make-VCat 500 5 "rechts") (make-VCham 
1032 5 "links"))) (make-VZoo (make-VCat 503 4.9 "rechts") (make-VCham 
1029 4.9 "links")))
(check-expect (tock (make-VZoo (make-VCat 500 5 "rechts") (make-VCham 
500 5 "links"))) (make-VZoo (make-VCat 503 4.9 "rechts")(make-VCham 497 
4.9 "links")))
(define (tock s)
   (cond
   [ (and ( < ( VCham-X (VZoo-VCham s)) bovengrens-cham ) (< (VCat-X 
(VZoo-VCat s)) bovengrens-cat) (string=? (VCham-R (VZoo-VCham s)) 
"rechts") (string=? (VCat-R (VZoo-VCat s)) "rechts"))
         (make-VZoo (make-VCat (+ (VCat-X (VZoo-VCat s)) 3) (- (VCat-H 
(VZoo-VCat s)) 0.1) "rechts")(make-VCham (+(VCham-X (VZoo-VCham s))3) 
(-(VCham-H (VZoo-VCham s)) 0.1) "rechts"))]
   [ (and ( > ( VCham-X (VZoo-VCham s)) bovengrens-cham ) (< (VCat-X 
(VZoo-VCat s)) bovengrens-cat) (string=? (VCham-R (VZoo-VCham s)) 
"rechts") (string=? (VCat-R (VZoo-VCat s)) "rechts"))
         (make-VZoo (make-VCat (+ (VCat-X (VZoo-VCat s) 3)  (- (VCat-H 
(VZoo-VCat s)) 0.1) "rechts")(make-VCham (VCham-X (VZoo-VCham s)) 
(-(VCham-H (VZoo-VCham s)) 0.1) "links"))]
    [ (and ( > ( VCham-X (VZoo-VCham s)) ondergrens-cham ) (< (VCat-X 
(VZoo-VCat s)) bovengrens-cat) (string=? (VCham-R (VZoo-VCham s)) 
"links") (string=? (VCat-R (VZoo-VCat s)) "rechts"))
         (make-VZoo (make-VCat (+ (VCat-X (VZoo-VCat s)) 3) (- (VCat-H 
(VZoo-VCat s)) 0.1) "rechts" )(make-VCham (-(VCham-X (VZoo-VCham s))3) 
(-(VCham-H (VZoo-VCham s)) 0.1) "links"))]
   ))


I see that + and later on -3 are always there and that happiness is 
always - 0,1

Now I can make auxilery functions :

add-happiness ( number)  increase-x (number)  decrease-x (number) etc. 
but then things are not more readable as now I believe.
But I wonder if I can make better auxilery functions.
I do know have the knowlegde to make itemization functions so that not a 
right answer for me.

I work in DrRacket with the beginning student language.

Roelof