Update order subtotal with jQuery

product.html

<div class="summary_block">
  <h3 id="title-price" content="574.8">Books - $574.80</h3>
  <form action="/cart/add" method="post" enctype="multipart/form-data" id="AddToCartForm">
    <div class="quantity">
      <div class="filter_cnt pull-left">
        <label for="Quantity">Quantity</label>
        <div class="filter">
          <select id="Quantity" name="quantity" class="selectpicker" tabindex="-98">
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
            <option value="5">5</option>
            <option value="6">6</option>
            <option value="7">7</option>
            <option value="8">8</option>
            <option value="9">9</option>
            <option value="10">10</option>
          </select>
        </div>
      </div>
    </div>
    <div class="clearfix"></div>
  </div>
  <div class="cost_block">
    <h3>Order Summary</h3>
    <p>Quantity: <span id="subtotal-quantity">4</span></p>
    <div class="clearfix"></div>
    <p>Subtotal: <span id="subtotal-amount">$2299.20</span></p>
  </div>
  <button type="submit" name="add" id="AddToCart" class="btn btn-primary">
    <span id="AddToCartText">Add to Cart</span>
  </button>
</form>
<div class="clearfix"></div>
</div>

subtotal.js

// demo: https://jsfiddle.net/chancesmith/4u7tdc3p/

//collect item's current price
var price = $('#title-price').attr("content");
//on quantity select change
$( "select#Quantity" )
  .change(function () {
    //grab new quantity
    var quantity = $(this).val();
  	//udpate subtotal box
      // update quantity
      // update subtotal
    $("#subtotal-quantity").text(quantity);
  	var newSubtotal = price * quantity;
  	$("#subtotal-amount").text( "$" + newSubtotal.toFixed(2) );
  })
  .change();