Repeater with automatic update columns

I've a repeater with values... I would like to allow users to modify VAT, Qt, Value and automatically calculate
SubTotal = Qt*Value
Total = SubTotal * (100+VAT)/100
 without page refresh... for example using ajax... can you help me??

 
 
 <asp:Repeater id="rptRighe" runat="server">
                <HeaderTemplate>
                <table border="1" width="100%">
                    <tr>
                        <th>Descrizione</th>
       ...