Pass in function which returns true or false into eloquent query context on a related property

There's an Employee model and many coveredArea models that belong to Employee.

Employee

int id
string name

CoveredArea

int id
int employee_id
decimal lat
decimal lng

I need to check if any of the coveredArea belonging to Employees are within 12km of latitude and longitude points contained in a collection of arrays called JobLocations and return these Employees.

public static function findClosest($jobLocations) {


    Employee::where('coveredareas',function($query) {

        $query->where(function($ca) { 

            $jobLocations->first(function($key, $val) {


                $m = DistanceCalculator::LatLngToLatLng($val['lat'],$val['lng'],$ca->lat, $ca->lng);
                  if($m <= 12000) return true;



        });  

        }

       )->first();
    }); 


}

I am unsure how to properly pass the LatLngToLatLng() function and lat and lng variables on the coveredAreas object that I presume should be on the $ca variable.

via Chebli Mohamed