$dayofweek = date('w', strtotime($date));
$result = date('Y-m-d', strtotime(($day - $dayofweek).' day', strtotime($date)));
$monday = strtotime('last monday', strtotime('tomorrow'));
$sunday = strtotime('+6 days', $monday);
echo "<P>". date('d-M-Y', $monday) . " to " . date('d-M-Y', $sunday) . "</P>";