parts of an audio slider

this is probably easier than i'm making it, but i'm not sure what my code needs to be for the previous button. i'm thinking i'll be able to use the next button script and just edit it a little. if someone could please look at this script and let me know what it needs to be that would be great (point me in the right direction). the script for the next button should be noticeable. i've tried to edit it to make it apply to the previous button, but i can't get it. as i said in my other post, my actionscript knowledge is minimal.