Laravel 5 Eloquent - adding calculated value as column to collection

I am calculating the distance of a teacher from a school.

I am querying the user table and then the userable_type teacher. The teacher table has the longitude and latitude values.

The following worked for me elsewhere when I query the teacher model directly but not when querying through the user model first!

            $query->whereHas('teacher', function ($query) use ($school) {

                $haversine = "(3961 * acos(cos(radians($school->latitude)) 
                    * cos(radians(latitude)) 
                    * cos(radians(longitude) 
                    - radians($school->longitude)) 
                    + sin(radians($school->latitude)) 
                    * sin(radians(latitude))))";

                $query->select() //pick the columns you want here.
                    ->selectRaw("{$haversine} AS distance")
                    ->whereRaw("{$haversine} < ?", '20');
                    // ->havingRaw('{$haversine}', '<', '20');

            });

The 'distance' field is not created but no errors are thrown! So my question is, in this scenario, how do I add the 'distance' value to each user as I would like to order by the distance?

Thanks, KH...

via Chebli Mohamed