calculation based on Quantity gravityforms

hello

I helpng a friend of mine to manage his calculation form in gravityforms.
But i′m stuck now.

You can order T-shirts based on the Quantity.
each Quantity has hes own price.

ex:
Quantity 1-24, print color 1 cost 22,50
Quantity 1-24, print color 2 cost 27,50
Quantity 25-49, print color 1 cost 17,50

and so on.

I try this one :
(({Quantity::16} / 1) * ({Quantity::16}/ 24)) * 22.50

And it doesent work ??

Is there any one that can help me, I have bin stuck now for 2 days.

PLEASE PLEASE