about laravel form calculation - php

Question

I had encountered the calculation in Laravel or maybe PHP stuff, I would like to ask for solution or maybe some others approach to get the things done.
These are the codes in the Model
public function getRedeemCount($member_id){
$count = DB::table('stamps')->where('user_id', '=', $member_id)->select('stamp_counter')->first();
return $count;
}
public function getFreeOfferCount($member_id){
$free_offer_count = DB::table('stamps')->where('user_id', '=', $member_id)->select('free_offer_counter')->first();
return $free_offer_count;
}
These are the codes in the Controller
public function redeemFreeOffer(Request $request)
{
$free_offer_counter = $request->input('minus_free_offer_counter');
$member_id = $request->input('sub_id');
$total_stamp_count = $this->userModel->getRedeemCount($member_id);
$free_offer_count = $this->userModel->getFreeOfferCount($member_id);
if(!$free_offer_count){
$insert_arr = array(
'user_id' => $member_id,
'free_offer_counter' => $free_offer_counter,
'created_at'=>date("Y-m-d H:i:s")
);
$stamps = DB::table('stamps')->insert($insert_arr);
if($stamps){
$arr = array('status' => 1,'message'=>'success','value'=>$free_offer_counter);
}
}
else {
$total_stamp_count->stamp_counter;
$total_free_offer_count = floor($total_stamp_count->stamp_counter/10);
$current_offer_count = $free_offer_count->free_offer_counter - $free_offer_counter;
$update_arr = array(
'free_offer_counter' => $current_offer_count,
'updated_at' => date("Y-m-d H:i:s")
);
$stamps = DB::table('stamps')->where('user_id', $member_id)->update($update_arr);
if ($stamps) {
$arr = array('status' => 1, 'message' => 'success', 'value' => $current_offer_count);
}
}
echo json_encode($arr);
}
Since I am using jQuery AJAX, so there's too much code, but I think it should be enough information for now. If it is insufficient, I will provide more in future.
The problem is how do I inject $total_free_offer_count into $current_offer_count? I do not have any columns that stored $total_free_offer_count.
$total_stamp_count->stamp_counter;
$total_free_offer_count = floor($total_stamp_count->stamp_counter/10);
$current_offer_count = $free_offer_count->free_offer_counter - $free_offer_counter;