Change dropdown based on another one in CodeIgniter - php

Question

I am new to CI. I need to Change some dropdown list according to another dropdown.
My controller code:
public function index()
{
$data = array();
$data['from_list'] = $this->from->list_from();
$data['to_list'] = $this->to->list_to();
$data['fromwhere_list'] = $this->fromwhere->list_fromwhere();
//$data['fromwhere_from_list'] = $this->fromwhere->list_fromwhere_from();
$data['towhere_list'] = $this->towhere->list_towhere();
$data['header'] = array('view'=>'header','data'=>array());
$data['main_content'] = array('view'=>'home','data'=>array());
$data['footer'] = array('view'=>'','data'=>array());
$this->load->view('template',$data);
//$this->load->view('home');
}
model code
function list_fromwhere()
{
$this->db->select('fromwhere_id,from_id,from_from_name');
$this->db->from('mt_from_from');
$query = $this->db->get();
return $query->result();
}
function list_from()
{
$this->db->select('from_id,from_name');
$this->db->from('mt_from');
$query = $this->db->get();
return $query->result();
}
My View code
<select class="" name="from" id="from" style="width: 20%;-webkit-border-radius: 3px;-moz-border-radius: 3px;border-radius: 3px;border: none;background: #dfe7eb;color: #999999;height: 38px;line-height: 38px;padding-left: 10px;padding-right: 20px;">
<?php
foreach($from_list as $from_item)
{
?>
<option value="<?php echo $from_item->from_id?>"><?php echo $from_item->from_name?></option>
<?php
}
?>
<!-- <option value="volvo">Airport</option>
<option value="saab">Town</option>
<option value="mercedes">Hotel</option> -->
</select>
<select class="" name="from_place" id="from_place" style="width: 56%;-webkit-border-radius: 3px;-moz-border-radius: 3px;border-radius: 3px;border: none;background: #dfe7eb;color: #999999;height: 38px;line-height: 38px;padding-left: 10px;padding-right: 20px;">
<?php
foreach($from_list as $from_item){
foreach($fromwhere_list as $fromwhere_item)
{
if($fromwhere_item->from_id == $from_item->from_id){
?>
<option value="<?php echo $fromwhere_item->fromwhere_id?>"><?php echo $fromwhere_item->from_from_name?></option>
<?php
}
}
}
?>
</select>
When we select the town, country by from dropdown list (firstone), I need to automatically change from place dropdown (secondone).