get selected form_dropdown codeigniter from database - codeigniter

Question

i am new with codeigniter, and i am trying to set selected value from database,
this code doesn't work,
<?php
$options = array(
'one' => 'one',
'two' => 'two',
);
$selected = $teach->number;
echo form_dropdown('number', $options, $selected);
?>
but when i try to manual, it work.
<?php
$options = array(
'one' => 'one',
'two' => 'two',
);
$selected = 'one';
echo form_dropdown('number', $options, $selected);
?>
I don't know why,
Any advice would be great. Thanks
this my controller
public function index() {
$this->load->helper('url');
$id = $this->uri->segment(3);
$this->data['teach'] = $this->EditTeachModel->getPosts(); // calling Post model method getPosts()
$this->data['singleTeach'] = $this->EditTeachModel->getPostsId($id); // calling Post model method getPosts()
//view
$this->load->view('edit_teach', $this->data); // load the view file , we are passing $data array to view file
}
public function update(){
$id = $this->input->post('kd');
$this->load->library('form_validation');
$data = array(
'kd' => $this->input->post('kd'),
'name' => $this->input->post('name'),
'date' => $this->input->post('date'),
'number' => $this->input->post('number'),
'pass' => $this->input->post('pass')
);
$this->EditTeachModel->updatePosts($id, $data);
$this->index();
}
This my model
public function getPosts(){
$this->db->from('teach');
$query = $this->db->get();
return $query->result();
}
public function getPostsId($data){
$this->db->select('*');
$this->db->from('teach');
$this->db->where('kd', $data);
$query = $this->db->get();
$result = $query->result();
return $result;
}
public function updatePosts($id, $data){
$this->db->where('kd', $id);
$this->db->update('teach', $data);
}
this my view
<?php foreach($singleTeach as $teach) {?>
<form method="post" action="<?php echo base_url() . "edit_teach/update"?>">
<div class="card-body"><td>
<div class="row">
<div class="col-6">
<div class="form-group">
<label id="kd">Kode :</label>
<input type="text" id="kd" name="kd" class="form-control" value="<?php echo $teach->kd; ?>">
</div>
<div class="form-group">
<label id="name">Nama:</label>
<input type="text" id="name" name="name" class="form-control" value="<?php echo $teach->name; ?>">
</div>
<div class="form-group">
<label id="date">Date :</label>
<input type="text" id="date" name="date" class="form-control" value="<?php echo $teach->date; ?>">
</div>
<div class="form-group">
<?php echo form_label('Number '); ?> <?php echo form_error('number'); ?>
<?php
$options = array(
'one' => 'one',
'two' => 'two',
);
$selected = $teach->number;
print_r($teach);
echo form_dropdown('number', $options, $selected);
?>
</div>
<div class="form-group">
<label id="pass">Password :</label>
<input type="text" id="pass" name="pass" class="form-control" value="<?php echo $teach->pass; ?>">
</div>
</div>
</div>
</div>
<!-- /.card-body -->
<div class="card-footer">
<?php echo form_submit(array('id' => 'submit','class'=> 'btn btn-primary', 'value' => 'Submit')); ?>
</div>
</form>
<?php } ?>