adding pixels to jquery .css() left property

This is my code:

var lef=$(this).css("left");
var top=$(this).css("top");
alert(lef);
$(this).after("<div class='edit cancel' style='position:absolute;top:"+top+";left:"+lef+"'>Cancel</div>");

Now the statement var lef=$(this).css("left") + 150, doesn't seem to work. I want to get the left property and add 150 pixels to it

How can i do this ?

Thanks.