Flash - Accessing A MovieClip's Property Within A Sprite (and Vice-versa)?

test.fla's document class is Test.as
test.fla's library has two MovieClips ThingMovieClip and Thing2MovieClip

I tried accessing the Thing.as public var thingState's property;

directly,

using something called Casting (??),

assigning an instance name,

but something that seemed so simple doesn't work,I commented the errors I got next to each way I tried,conversely how would I access the MovieClip Thing2MovieClip from Thing.as (which is a child of Test.as because that's where it's instantiated), it just doesn't recognise an object of its parent exists, here are the 2 classes:

package com.hello.test.test
{
import flash.display.Sprite;
import flash.events.Event;[code]........

I think i'm missing some basic but fundemental understanding of ActionScript 3 and I have no other knowledge of other scripting /programming languages either.when I follow tutorials exactly they seem simple enough, but then start applying what I think is logical usage then it throws up errors..