$(function() {

      $(".button").click(function() {
        var $button = $(this);
        var oldValue = $button.parent().find("input").val();
    
        if ($button.text() == "+") {
    	  var newVal = parseFloat(oldValue) + 6;
    	  // AJAX save would go here
    	} else {
    	  // Don't allow decrementing below zero
    	  if (oldValue >= 7) {
    	      var newVal = parseFloat(oldValue) - 6;
    	      // AJAX save would go here
    	  }
    	}
    	$button.parent().find("input").val(newVal);
    });

});