Play in reverse help

1

Thanks to greenLantern, who pointed out i am an idiot :S, i am trying to use the function:

MovieClip.prototype.goBackwards = function(frames) {
		this.onEnterFrame = function() {
				this.gotoAndStop(this._currentframe - 1);
				frames -= 1;
				if (frames == 0) {
						delete this.onEnterFrame;
				}
		}
}

So that when a user clicks on a button the movie cilp plays in reverse for 15 frames, but right now nothing happens when they click on the button. The code for my button is:

on (release) {
_root.lessons_mc.goBackwards(15);
}

Any help? Thanks, jesse
the fla can be found at http://www.norcaldesigns.com/jesse/wp_101.fla