Return a value to one function from another [closed]

I have 2 functions in PHP and i want to return a value to one function to another. this is my functions

 public function save_payment_log_data($icasl_number, $exam_session) {$paylog_av = $this->payment_log_exists($icasl_number, $exam_session);}function payment_log_exists($icasl_no, $exam_session) {        $this->db->where('icasl_no', $icasl_no);        $this->db->where('exam_session', $exam_session);        $query = $this->db->get('exm_paymentlog');        if ($query->num_rows() > 0) {            $pl = $query->row();            $pay_id = $pl->paylog_id;            return $pay_id;        } else {            return false;        }    }

I want to return $pay_id to the save_payment_log_data() function but in here $pay_id didn't return to that function. I think it's return from the function payment_log_exists()so how can I return $pay_id to the save_payment_log_data() function