2つの配列から、新しい配列を作成

コード

$a = array(
  "3"  => 3,
  "42" => 15,
  "4" => 22,
  "88"  => 6,
);

$b = array(
  "0" => array(
              "id" => 42,
              "area" => "東京",
  ), 
  "1" => array(
              "id"  => 88,
              "area" => "大阪",
  )
);

print_r($a); 
print_r($b); 

$c = array();
for($i = 0;$i < count($b);$i++){
  $c[$b[$i]['id']]['num'] = $a[$b[$i]['id']];
  $c[$b[$i]['id']]['area'] = $b[$i]['area'];
}

print_r($c);
	
foreach($c as $key => $val){ 
  echo $key."　"; 
}