code: public static function getWeek(int $iWeek, int $iYear, string $sFormat = "Y-m-d") : Date
      {
          $iFirstDayInYear = date("N",mktime(0, 0, 0, 1, 1, $iYear));
  
          if ($iFirstDayInYear < 5) { $iShift = -($iFirstDayInYear - 1) * 86400; } else { $iShift = (8 - $iFirstDayInYear) * 86400; }
  
          if ($iWeek > 1) { $iWeekInSeconds = ($iWeek-1) * 604800; } else { $iWeekInSeconds = 0; }
  
          $iTimestamp = mktime(0, 0, 0, 1, 1, $iYear) + $iWeekInSeconds + $iShift;
          $iTimestampLastDay = mktime(0, 0, 0, 1, 6, $iYear) + $iWeekInSeconds + $iShift + 604800;
  
          return array(date($sFormat, $iTimestamp), date($sFormat, $iTimestampLastDay));
      }
docs: set name of image
  
  @access public
  @param  int $iWeek number of week
  @param  int $iYear year
  @param string $sFormat
  @return Date