Label to display total of TextBox

Hi I've got this code, I want the amount_01 label to calculate area_01 * rate_01 when values are entered into the TextBox, I've looked and tried everything. Please someone help:


</p><p>&lt;tr&gt;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;td&gt;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;asp:TextBox ID="desc_01" runat="server" Width="320px" BorderStyle="None" BackColor="#ffffcc" /&gt;&lt;/td&gt;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;td&gt;
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