如何计算$('.shipping').val(zona);和$('#pay').text(total.toFixed(3));
然后将结果放入像下面脚本中的<span class='amount'></span>这样的span元素中

<script> 
$(document).ready(function() {
  $("select.area").change(function() {
    var zone = $(this).children("option:selected").val();
    var area = $(this).children("option:selected").text();
    $('.shipping').val(zone);
    $('.address').val(area);
  });
});

function updateTotalPrice() {
  var qty = parseInt($('#qty').val(), 10);
  var price = parseFloat($('#price').attr('value'));
  var total = qty * price;
  $('#pay').text(total.toFixed(3));
  $('#qty').text(total);
}

$(document).ready(function() {
  // set up event listeners 
  $('#plus-btn').click(function(event) {
    increaseCount(event, this);
  });
  $('#minus-btn').click(function(event) {
    decreaseCount(event, this);
  });
  $('#qty').change(function(event) {
    updateTotalPrice();
  });

  // update total price on page load 
  updateTotalPrice();
});

</script>