JSFiddle - React, Tailwind, and code Playground

HTML

<table>
<thead>
<tr>
<th>Particulars</th>
<th>Packing</th>
<th>Quantity</th>
<th>Rate</th>
<th>Amount</th>
</tr>
</thead>
<tr>
<td>1</td>
<td>1</td>
<td>
 <input type='text' class='quantity' style='width:80%;' value=''/> 
</td>
<td><input type="text" name="rate" style='width:35%;'></td>
<td><input type='text' style='width:100%;' class='amount' readonly=''/></td>
</tr>
<tr>
<td>1</td>
<td>1</td>
<td>
<input type='text' class='quantity' style='width:80%;' value=''/>
</td>
<td><input type="text" name="rate"></td>
<td><input type='text' style='width:100%;' class='amount' readonly=''/></td>
 </tr>
<tr>
<td>1</td>
<td>1</td>
<td>
<input type='text' class='quantity' style='width:80%;' value=''/>
</td>
<td><input type="text" name="rate"></td>
<td><input type='text' style='width:100%;' class='amount' readonly=''/> </td>
</tr>
</table>

JavaScript

$('input[name=rate]').on('blur',function(){
   var rate=$(this).val();
   var quantity = $(this).parent().parent().find('.quantity').val();
   var amount = rate*quantity;
   $(this).parent().parent().find('.amount').val(amount);
});