<?php
 
error_reporting(-1);
 
$amount = 54500;
 
$bills = array(
	100    =>    23,
	500    =>    5,
	1000   =>    0,
	5000   =>    200
);
$bills = array_reverse($bills);
$array = array();
foreach ($bills as $nominal => $value) {
		$countBanknote = floor($amount / $nominal);
                  if($amount >= $nominal and $countBanknote < $value) {
	     	$value = $value - $countBanknote;
	     	$amount = $amount % $nominal;
	     	$return = "{$nominal} x {$countBanknote}";
	     	$array[] = $return;
	     	var_dump($bills);
	   }
   }
$array = implode(" ", $array);
echo $array;

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