How to pass variable with ajax?

 <meta charset="UTF-8">
 <title>View applications</title>
 <link href="style.css" rel="stylesheet" type="text/css">
<?php require_once ('includes/db.php') ?>
 <script type="text/javascript" src="module/jquery-3.2.1.min.js"></script>

the <script>
$(document).ready(function(){
$("#rat").submit(function(){
 var ocenka = prompt ("Enter text: ")
$.ajax({
url:"includes/functions.php",
type:"POST",
 data:({rat: ocenka, action: "close"}),
 dataType: "html"
});
});
});
</script>




<?php require_once ('includes/header.php'); ?>

<?php 
$qr_result = mysqli_query($connection, "SELECT * FROM `applications` WHERE `id` =" . (int) $_GET['id']);

$data = mysqli_fetch_assoc($qr_result);

?>
 <form action="includes/functions.php" method="POST">

 <div class="buttons">
 <input type="hidden" name="action" value="delete">
 <input type="hidden" name="id" value="<?php" echo $_get['id'] ?> />
 <input type="submit" value="Delete application">
</div>
</form>
 <form action="includes/functions.php" method="POST">
the <div>
 <input type="hidden" name="action" value="close">
 <input type="hidden" name="id" value="<?php" echo $_get['id'] ?> />
 <input type="submit" id="rat" value="Close the application">
</div>
</form>
 <div class="head">
 <label class="bold"> application Status </label> <br>
 <label id="change"> <?php echo $data['status']; ?> </label><br><br>
</div>
 <div class="head">
 <label class="bold"> Subject application </label> <br>
 <label> <?php echo $data['theme']; ?> </label><br><br>
</div>

 <div class="head">
 <label> Description </label> <br>
 <label> <?php echo $data['text']; ?> </label><br><br>
</div>
 <div class="head">
 <label class="bold"> Assigned to </label> <br>
 <form action="includes/functions.php" method="POST">
<?php require_once ('includes/db.php');
$usersel = mysqli_query($connection, "SELECT * FROM `user`");
echo "<select id='selUser' name = 'selUser'-->";
while ($data =mysqli_fetch_assoc($usersel)){
 echo '<option>' . $data['fullname'] . '</option>';
 } 
echo "<input type="hidden" name="action" value="update">";
echo "<input type="hidden" name="id" value="" . $_GET[" id'] . "'>";
echo "<input type="submit" value="Accept">";
 ?> 
</form>
br><br>
</div>

<?php

$location = '/';
echo "Ocenka:" . $_POST['rat'] . "</br-->";
if (isset($_POST['action']))
{
require_once('db.php');

 $query = ";

switch($_POST['action'])
{
 case 'addApp':
 $theme = $_REQUEST['theme'];
 $text = $_REQUEST['text']; 
 $query = "INSERT INTO `applications` (`theme`, `text`) VALUE('$theme', '$text')";
break;

 case 'delete':
 $query = "DELETE FROM `applications` WHERE `id` =" . $_POST['id'];
break;

 case 'addUser';
 $fullname = $_REQUEST['fullname'];
 $query = "INSERT INTO `user` (`fullname`) VALUE('$fullname')";
break;

 case 'update';
 $query = "UPDATE `applications` SET `associate` = '" . $_POST['selUser'] . "' WHERE `id` = " . $_POST['id'];
break;

 case 'close';
 $query = "UPDATE `applications` SET `status` = 'Closed' `assessment` = ". $_POST['rat'] . "WHERE `id` =" . $_POST['id'];
break;
}

 if (!empty($query)) mysqli_query($connection, $query);
}
print_r($query);
//header ('Location:' . $location);
exit();