Future Dates

<?php
date_default_timezone_set('Europe/Sofia');
$numbersStr = $_GET['numbersString'];
$dateStr = $_GET['dateString'];

preg_match_all('/[\W_]+?(\d+)[\W_]+?/', $numbersStr, $numbersArr);
$numbersArr = $numbersArr[1];
$backwardsSum = 0;
foreach ($numbersArr as $number) {
    $backwardsSum += (int)$number;
}

$backwards = $backwardsSum;
if ($backwardsSum > 9) {
    $backwards = (int)strrev('' . $backwardsSum);
}

preg_match_all('/\d{4}\-\d{2}\-\d{2}/', $dateStr, $datesArr);
$datesArr = $datesArr[0];

if (count($datesArr) === 0) {
    die('<p>No dates</p>');
}

echo '<ul>';
foreach ($datesArr as $dateStr) {
    $date = new DateTime($dateStr);
    date_add($date, date_interval_create_from_date_string($backwards . ' days'));
    $resultDate = $date->format('Y-m-d');
    echo "<li>{$resultDate}</li>";
}
echo '</ul>';