i want to compute specific field in my db depends on ID_number : This is my model

```
public function total_late()
	{
		
		$query = "SELECT sum(late_deduction) as late_deduction FROM tbl_dtr";
		$result = $this->db->query($query);
		return $result->row()->late_deduction;
	}
```
this the image of db
[enter image description here][1]


this is the image of my table
[enter image description here][2]


  [1]: https://i.stack.imgur.com/ViMUi.png
  [2]: https://i.stack.imgur.com/6zH1M.png

please help asap

thank you in advance