Problems with parents and post function

Problems with parents and post function

Hello;
I have a problem with this code, i don't know how change carpeta value with returned data only in the changed select. 
$(document).ready(function() {
$(".categorias").change(function(){
            kid=$(this).parents('.parrafo').find('.categorias').val();
            $.post("modules/vercategoria.php",{ 
action: "mostrarcarpeta",
id: kid}  
                ,function(data){
              HERE: $(this).parents('.parrafo').find('.categorias').val(data);
});})

<div id="parrafo>
<select class='categorias' name='categorias' width='90%' style='width: 90%'  >
Here the options of the select
</select>
<input class='carpeta' type='text' name='carpeta' value='' '/>
</div>

<div id="parrafo>
<select class='categorias' name='categorias' width='90%' style='width: 90%' >
Here the options of the select
</select>
<input class='carpeta' type='text' name='carpeta' value='' '/>
</div>