Tricky maths question

[EvilKris]

First off, thanks to Malee and co for solving my arrow rotation problem before- working great now.


I've been stumped by something else now. Maths never was my strong point in school.

Check out the example pic. As you can see, the archer fires the arrow into basically a wall mc.
TARGETA= invisible bounding rectangle within the target stand that runs hitTests for the arrow and stops it when it lands.
TARGETB=frontal perspective view of the target.

What I want to happen;- the arrow hits TARGETA and then a hole (black circle mc) appears somewhere on TARGETB to represent approximately where it has landed.
In code-
- There's no real z depth to the arrow so I'll have to randomize the x position on TARGET B. But the arrow hits TARGETA mc at a certain _y position so I can then use that _y value to estimate a _y position for the hole mc.

So my question is how do I transfer the y position of the arrow to a suitable y position on TARGET B mathematically? TARGET A and TARGET B are both different heights, and also the target stand is at random locations so I'd have to do something about it's x position.

Like, convert all the mcs to global x,y and targeta._height-targetb_height+arrow._y?
Tried all sorts but nothing is working accurately right now.