通过将x天添加到上一个日期来查找确切日期

<?php
     $today = "2017-06-14";
     $prev = "1994-06-01";
     $date = $prev + //keep on adding 60 days till june,2017 
     echo '<br>' .$date;
?>
<?php
     $today = "2017-06-14";
     $prev =