making map layer visible in flex api

Hi there
I have published a map as map service on ARCGIS server as map service. I access it using flex api 3.0.. I want to know is there any way I can change the visibility of layer in the map. for example on click of a button i want to visible a layer in the map. here is how i used the published service,
<esri:Map id="myMap" layoutDirection="ltr" mapClick="mapClickHandler(event)">

<esri:ArcGISTiledMapServiceLayer url="http://localhost:6080/arcgis/rest/services/mymap/MapServer"/>

<esri:GraphicsLayer id="clickGraphicsLayer"/>
</esri:Map>

mymap has 7 layers i want to make layer6 visible on mouse click. any suggestion is appreciated.
rgds
nadeem