[Solved] JavaScript calculation Error NaN

below in my text field

but displaying NaN in text field

<div class="col-md-4">
    <div class="form-group">
        Untit Price  :
        <input type="text" style="text-align:right;" readonly="readonly" id="txtUnitPrice" value="0.00" name="UnitPrice" class="form-control" />
    </div>
</div>
<div class="col-md-4">
    <div class="form-group">
        Qunantity  :
        <input type="text" id="txtQuantity" style="text-align:right;" value="0.00" name="Quantity" class="form-control" />
    </div>
</div>
<div class="col-md-4">
    <div class="form-group">
        Discount  :
        <input type="text" id="txtDiscount" style="text-align:right;" value="0.00" name="Discount" class="form-control" />
    </div>
</div>

using JS for calculation

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<link rel="shortcut icon" href="#">
<script type="text/javascript">
    $(document).ready(function () {
        $("#select2-3").val(0);
        $("#select2-3").change(function () {
            var itemId = $("#select2-3").val();
            GetItemUnitPrice(itemId);
        });
        
        $("input[type=text]").change(function() {
            CalculateSubTotal();         
        });
    });
 
    function CalculateSubTotal() {
        var UnitPrice = $("txtUnitPrice").val();
        var Quantity = $("txtQuantity").val();
        var Discount = $("txtDiscount").val();
 
        var Total = (UnitPrice * Quantity) - Discount;
        $('#txtTotal').val(parseFloat(Total).toFixed(5));
    }
 
    function GetItemUnitPrice(itemId) {
        $.ajax({
            async: true,
            type: 'GET',
            dataType: 'JSON',
            contentType: 'application/json; charset=utf-8',
            url: '/Home/getItemUnitPrice', data: { itemId: itemId },
            success: function (data) {
                $("#txtUnitPrice").val(parseFloat(data).toFixed(2));
            },
            error: function () {
                alert("There is some problem to get the Unit Price.");
            }
        });
    }
</script>