Fatal error: Uncaught Error: Unsupported operand types

I need your help please. I got an error about "Unsupported operand types" but i didn't know about it. i've been trying search on google but i'm still can't fix it.

this my error title :

Fatal error: Uncaught Error: Unsupported operand types in /Applications/XAMPP/xamppfiles/htdocs/aplikasi_penjualan/admin/barang.php:28 Stack trace: #0 {main} thrown in /Applications/XAMPP/xamppfiles/htdocs/aplikasi_penjualan/admin/barang.php on line 28

and this my code :

<?php include 'header.php'; ?>

<h3><span class="glyphicon glyphicon-briefcase"></span>  Data Barang</h3>
<button style="margin-bottom:20px" data-toggle="modal" data-target="#myModal" class="btn btn-info col-md-2"><span class="glyphicon glyphicon-plus"></span>Tambah Barang</button>
<br/>
<br/>

<?php 
$periksa=mysqli_query($conn, "select * from barang where jumlah <=3");
while($q=mysqli_fetch_array($periksa)){ 
        if($q['jumlah']<=3){ 
                ?>   
                <script>
                        $(document).ready(function(){
                                $('#pesan_sedia').css("color","red");
                                $('#pesan_sedia').append("<span class='glyphicon glyphicon-asterisk'></span>");
                        });
                </script>
                <?php
                echo "<div style='padding:5px' class='alert alert-warning'><span class='glyphicon glyphicon-info-sign'></span> Stok  <a style='color:red'>". $q['nama']."</a> yang tersisa sudah kurang dari 3 . silahkan pesan lagi !!</div>";     
        }
}
?>
<?php 
// $per_hal=10;
$jumlah_record=mysqli_query($conn, "SELECT COUNT(*) from barang");
$jum=mysqli_fetch_array($jumlah_record);
$halaman= ceil($jum / $per_hal);  //-----> THE ERROR IN HERE
$page = (isset($_GET['page'])) ? (int)$_GET['page'] : 1;
$start = ($page - 1) * $per_hal;
?>
<div class="col-md-12">
        <table class="col-md-2">
                <tr>
                        <td>Jumlah Record</td>              
                        <td><?php echo $jum; ?></td>
                </tr>
                <tr>
                        <td>Jumlah Halaman</td>     
                        <td><?php echo $halaman; ?></td>
                </tr>
        </table>
        <a style="margin-bottom:10px" href="lap_barang.php" target="_blank" class="btn btn-default pull-right"><span class='glyphicon glyphicon-print'></span>  Cetak</a>
</div>
<form action="cari_act.php" method="get">
        <div class="input-group col-md-5 col-md-offset-7">
                <span class="input-group-addon" id="basic-addon1"><span class="glyphicon glyphicon-search"></span></span>
                <input type="text" class="form-control" placeholder="Cari barang di sini .." aria-describedby="basic-addon1" name="cari"> 
        </div>
</form>
<br/>
<table class="table table-hover">
        <tr>
                <th class="col-md-1">No</th>
                <th class="col-md-4">Nama Barang</th>
                <th class="col-md-3">Harga Jual</th>
                <th class="col-md-1">Jumlah</th>
                <!-- <th class="col-md-1">Sisa</th>               -->
                <th class="col-md-3">Opsi</th>
        </tr>
        <?php 
        if(isset($_GET['cari'])){
                $cari=mysqli_real_escape_string($_GET['cari']);
                $brg=mysqli_query($conn, "select * from barang where nama like '$cari' or jenis like '$cari'");
        }else{
                $brg=mysqli_query($conn, "select * from barang limit $start, $per_hal");
        }
        $no=1;
        while($b=mysqli_fetch_array($brg)){

                ?>
                <tr>
                        <td><?php echo $no++ ?></td>
                        <td><?php echo $b['nama'] ?></td>
                        <td>Rp.<?php echo number_format($b['harga']) ?>,-</td>
                        <td><?php echo $b['jumlah'] ?></td>
                        <td>
                                <a href="det_barang.php?id=<?php echo $b['id']; ?>" class="btn btn-info">Detail</a>
                                <a href="edit.php?id=<?php echo $b['id']; ?>" class="btn btn-warning">Edit</a>
                                <a onclick="if(confirm('Apakah anda yakin ingin menghapus data ini ??')){ location.href='hapus.php?id=<?php echo $b['id']; ?>' }" class="btn btn-danger">Hapus</a>
                        </td>
                </tr>             
                <?php 
        }
        ?>
        <tr>
                <td colspan="4">Total Modal</td>
                <td>                      
                <?php 
                
                        $x=mysqli_query($conn, "select sum(modal) as total from barang");       
                        $xx=mysqli_fetch_array($x);                     
                        echo "<b> Rp.". number_format($xx['total']).",-</b>";               
                ?>
                </td>
        </tr>
</table>
<ul class="pagination">                   
                        <?php 
                        for($x=1;$x<=$halaman;$x++){
                                ?>
                                <li><a href="?page=<?php echo $x ?>"><?php echo $x ?></a></li>
                                <?php
                        }
                        ?>                                           
                </ul>
<!-- modal input -->
<div id="myModal" class="modal fade">
        <div class="modal-dialog">
                <div class="modal-content">
                        <div class="modal-header">
                                <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
                                <h4 class="modal-title">Tambah Barang Baru</h4>
                        </div>
                        <div class="modal-body">
                                <form action="tmb_brg_act.php" method="post">
                                        <div class="form-group">
                                                <label>Nama Barang</label>
                                                <input name="nama" type="text" class="form-control" placeholder="Nama Barang ..">
                                        </div>
                                        <div class="form-group">
                                                <label>Jenis</label>
                                                <input name="jenis" type="text" class="form-control" placeholder="Jenis Barang ..">
                                        </div>
                                        <div class="form-group">
                                                <label>Suplier</label>
                                                <input name="suplier" type="text" class="form-control" placeholder="Suplier ..">
                                        </div>
                                        <div class="form-group">
                                                <label>Harga Modal</label>
                                                <input name="modal" type="text" class="form-control" placeholder="Modal per unit">
                                        </div>    
                                        <div class="form-group">
                                                <label>Harga Jual</label>
                                                <input name="harga" type="text" class="form-control" placeholder="Harga Jual per unit">
                                        </div>    
                                        <div class="form-group">
                                                <label>Jumlah</label>
                                                <input name="jumlah" type="text" class="form-control" placeholder="Jumlah">
                                        </div>                                                                                                                                    

                                </div>
                                <div class="modal-footer">
                                        <button type="button" class="btn btn-default" data-dismiss="modal">Batal</button>
                                        <input type="submit" class="btn btn-primary" value="Simpan">
                                </div>
                        </form>
                </div>
        </div>
</div>



<?php 
include 'footer.php';

?>

I Hope you can help me.. Thanks a lot.