как вычитать '.$row["kg"].'-'.$row["tara"].'?

<?php
//fetch.php
include('database_connection.php');

$query = "SELECT * FROM sample_data ORDER BY id ASC";

$statement = $connect->prepare($query);
$statement->execute();
$result = $statement->fetchAll();
$total_row = $statement->rowCount();
$output = '';

if($total_row > 0)
{
foreach($result as $row)
{

$output .=

'
<tr>

<td>'.$row["id"].'</td>
<td>'.$row["country"].'</td>
<td>'.$row["kg"].'</td>
<td>'.$row["tara"].'</td>



</tr>
'
;
}
}
else
{
$output .= '
<tr>
<td colspan="3" align="center">Пусто</td>
</tr>
';
}

echo $output;

?>