How Do I Perform Calculations Using Jquery In Asp.Net C#

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C#

ASP.NET

bootstrap

Hello friends i am trying to do some basic calculations using jquery such rate into quantity minus discount percentage and add tax percentage like as follows i write the following code for that but i not working properly i want a suggestion from you please suggest me to do calculations
and Thanks in advance for always helping me..!

Here Is My jquery code

<script type="text/javascript">
$(function () {
$("[id*=txt_part_quantity]").keypress(function () {

var price = parseFloat($("[id*=txt_part_rate]").val());
var Qnt = parseFloat($("[id*=txt_part_quantity]").val());
var total = parseFloat(price * Qnt);
$("[id*=txt_net_taxable_amt]").val(total);

/* When I entered a quantity then I get NaN in a TextBox Net Taxable Amount and in Discount Amount */

var dis = parseFloat($("[id*=txt_discount_percentage]").val());
var dis_amt = parseFloat(total * dis) / 100;
$("[id*=txt_discount_amount]").val(dis_amt);
var net_amt = amt - dis_amt;
$("[id*=txt_net_taxable_amt]").val(net_amt);
});
});
</script>

<script type="text/javascript">
    $(document).ready(function () {
        $("#ddl_vat").change(function () {
            getVal();
        });
        getVal();
    });
    function getVal() {
        var a = $('#ddl_vat:selected').text();

    };
    </script>

and here is my C# ASP.NET Web Form

<div class="form-group col-md-5">
    <label>
        Part Rate :
    </label>
    <asp:TextBox ID="txt_part_rate" runat="server" CssClass='form-control' placeholder="Part Rate" ClientIDMode="Static"></asp:TextBox>
</div>
<div class="form-group col-md-5">
    <label for="exampleInputPassword1">
        Part Quantity :
    </label>
    <asp:TextBox ID="txt_part_quantity" runat="server" CssClass='form-control' ClientIDMode="Static"
        placeholder="Part Quantity"></asp:TextBox>
</div>
<div class="form-group col-md-5">
    <label>
        Discount Percentage :
    </label>
    <asp:TextBox ID="txt_discount_percentage" runat="server" CssClass='form-control' placeholder="Discount Percentage" ClientIDMode="Static"></asp:TextBox>
</div>
<div class="form-group col-md-5">
    <label>
        Discount Amount :
    </label>
    <asp:TextBox ID="txt_discount_amount" runat="server" CssClass='form-control' placeholder="Discount Amount" ClientIDMode="Static"></asp:TextBox>
</div>
<div class="form-group col-md-5">
    <label>
        Net Taxable Amount :
    </label>
    <asp:TextBox ID="txt_net_taxable_amt" runat="server" CssClass='form-control' placeholder="Net Taxable Amount" ClientIDMode="Static"></asp:TextBox>
</div>
<div class="form-group col-md-5">
<label>
    TAX :
</label>
<asp:DropDownList ID="ddl_vat" runat="server" CssClass='form-control' ClientIDMode="Static">
</asp:DropDownList>
</div>
<div class="form-group col-md-5">
    <label for="exampleInputPassword1">
        TAX Amount :
    </label>
    <asp:TextBox ID="txt_vat_amount" runat="server" CssClass='form-control' placeholder="VAT Amount" ClientIDMode="Static"></asp:TextBox>
</div>
<div class="form-group col-md-5">
    <label>
        Total Amount :
    </label>
    <asp:TextBox ID="txt_total_amt" runat="server" CssClass='form-control' placeholder="Total Amount" ClientIDMode="Static"></asp:TextBox>
</div>

Please help me to do this
Thanks a lot for your time and your support