Proportional object scaling with percentage slider

I’ve been trying to figure out how to do this:

I need to use a horizontal slider 400 pixels wide that scales another movieclip (rectangle) proportionally based on percentage…the left end of the slider is min (0%) and right end is max (100%). If the slider is moved to 100%, the rectangle clip scales up proportionally to the maximum width of 400 pixels. If the slider is moved to 0%, the width of rectangle scales down to the minimum width of 100 pixels.

Any help would be greatly appreciated!