If you want to merge two columns and add data to them you can use colspan attribute.
<table>
<tr>
<th>Item Name</th>
<th>Price</th>
</tr>
<tr>
<td>Item 1</td>
<td>$100</td>
</tr>
<tr>
<td>Item 2</td>
<td>$80</td>
</tr>
<tr>
<td colspan="2">Sum: $180</td>
</tr>
</table>