ขอสอบถาม code php บวก วันเดือนปี ครับ เช่น 2015-10-01 + 4 ปี = 2019-10-01

$olddate='2015-10-01';
$result_date = strtotime('+4 year', strtotime($olddate));

<?php do { ?>
    <tr>
      <td><?php echo $row_Recordset1['SN']; ?></td>
      <td><?php echo $row_Recordset1['name']; ?></td>
      <td><?php echo $row_Recordset1['model']; ?></td>
      <td><?php echo $row_Recordset1['forwork']; ?></td>
      <td align="center"><?php echo $row_Recordset1['waranty']; ?></td>
      <td><?php echo $row_Recordset1['IV']; ?></td>
      <td><?php echo $row_Recordset1['vendor']; ?></td>
      <td><?php echo $row_Recordset1['date']; ?></td>
      <td></td>
    </tr>

<td><?php echo strtotime("+".$row_Recordset1['waranty']." year", strtotime($row_Recordset1['date']));?></td>

<?php do { ?>
    <tr>
      <td><?php echo $row_Recordset1['SN']; ?></td>
      <td><?php echo $row_Recordset1['name']; ?></td>
      <td><?php echo $row_Recordset1['model']; ?></td>
      <td><?php echo $row_Recordset1['forwork']; ?></td>
      <td align="center"><?php echo $row_Recordset1['waranty']; ?></td>
      <td><?php echo $row_Recordset1['IV']; ?></td>
      <td><?php echo $row_Recordset1['vendor']; ?></td>
      <td><?php echo $row_Recordset1['date']; ?></td>
      <td><?PHP echo date('Y-m-d', strtotime($row_Recordset1['date']."+".$row_Recordset1['waranty']." year")); ?></td>
    </tr>

<td><?php echo date("Y-m-d", strtotime("+".$row_Recordset1['waranty']." day", strtotime($row_Recordset1['date'])));?></td>