<?php
/** solving https://youtu.be/WiB2_dXSSMg */
function reorder($a)
{
   if(count($a) <=1)
   {
      yield $a;
   }
   else
   {
      foreach($a as $k => $v)
      {
         $x = array($k => $v);
         $b = $a;
         unset($b[$k]);
         foreach(reorder($b) as $c)
         {
            yield $c + $x;
         }
      }
   }
}

$n = range(1, 9);

foreach(reorder($n) as $cn)
{
   $a = array_values($cn);
   $s = $a[0] +13*$a[1]/$a[2] +$a[3] +12*$a[4] -$a[5] -11 +$a[6]*$a[7]/$a[8] - 10;
   /* if($s == 66) */
   if($s > 65.999 AND $s < 66.001)
   {
      echo "{$a[0]} + 13x{$a[1]}/{$a[2]} + {$a[3]} + 12x{$a[4]} - {$a[5]}";
      echo " - 11 + {$a[6]}x{$a[7]}/{$a[8]} - 10 = {$s}" . PHP_EOL;
   }
}