array keys

<?php
 $a = array('1' =>"abc", '3' => "fgh", '5' => "fgh", '7' =>"dfg", '9' => "jhk", '11' => "ioo");
$b = array('3' =>"abc", '6'=> "fgh", '9' => "dfg");
$key=array();
foreach ($b as   $v){
    if(in_array($v, $a))
    {
        $n=  array_search($v, $a);
        $x=array_keys ($a,$v);print_r($x);
        $key=array_merge($key,$x);
    }
}

echo '<pre>';print_r($key);


ini jawabannya