adding two values together

I am converting a asp vbscript site to aspx c#
I am stuck on how to covnvert the below used on the old site into the apsx c# page

Any help appreciated

<input name="requires" type="text" class="ms-stylebox2" id="requires" value="<%=((rs_bom.Fields.Item("usage_quantity").Value)* (kitqty))%>" size="15">
...