Select data of a specific related item to se in a calculation field.

Hi,

I'm trying to use data of a specific related item that matches a certain criteria (because there are multiple items referenced) to use i a calculation field.

For example :

X = item 1 APP A,

Y = item 1 APP B,

Z = item 2 APP B 

D = date field APP B

T = text field APP B

Both Y and Z  are related to X

In X, i would like to show T of Y or Z that has the most recent D.  

Anybody know how to do this?