Drag and Drop using targets

I have created 6 dragable movie clips using the tutorial I found here. I also have the “drop zone”. What i need to try and do with some more code is only allow the 6 movieclips to be dragged onto the dropzone in 1 correct order. If it is correct it disappears, if incorrect it gets placed away from the dropzone. I have no idea where to start with the code, any help would be greatly appreciated.

Thanks