Merge and transpose the data from two json strings containing flat array structures

I have two JSONs which both have the same keys and I want to merge them based on their related keys.

My first json: {"3":"test","4":"exam"}

My second json: {"3":"12","4":"19"}

I want to have an array like this:

array("final") {
 [3]=> {
   "name" => "test"
   "quantity" => "12"
  } 
  [4]=> {
   "name" => "exam"
   "quantity" => "19"
  } 
}  

Decode the json objects to array

 $x = json_decode($x);
 $y = json_Decode($y);
 $res['final'] = [];
 foreach($x as $key => $value)
 {
  foreach($y as $k => $v)
  {
    if($key == $k)
    {
        $res['final'][$key]['name'] = $value;
        $res['final'][$key]['quantity'] = $v;
    }
  }
 }
 print_r($res);

Output will be

Array
(
[final] => Array
    (
        [3] => Array
            (
                [name] => test
                [quantity] => 12
            )

        [4] => Array
            (
                [name] => exam
                [quantity] => 19
            )

    )

)