Calculate Zoom effect

hey all,

Like my earlyest thread i am wroking on a 3d zoom function…
how can i calculate it it best?

i have a placeholder_mc:
width: 400

in the placeholder_mc i have 10 obj_mc’s:
orig width:400, scaled in placeholder_mc: _xscale=20
orig height:400, scaled in placeholder_mc: _yscale=20

the _x and _y are random positions

Now i need a formula that make the placeholder_mc zoom into obj_mc inside of him… and the placeholder_mc must be _xscaled, _yscaled so that the width and height of the clicked _mc are exaclty 400x400

for the _x and _y i use… onEnterframe=

so this makes the placeholder_mc move to the correct postion of the clicked object but how can i scale it now he placeholder_mc so that he moves and scales correct?

hehe i know it is a crappy explanation but anyhelp? please…