PHP - Field Calculation Formula

This code, that I didn't write, but am trying to modify, generates the cost of a video purchase.

One line (line 32) is a formula , I believe for setting a purchase price amount:

$amout += $video->video_play_price?$video->video_play_price:$video_cost;

Another line (line 50) is a formula for deducting to create another amount:

 $uploader_amount = $video_cost - $charge;

I think line 50 is correct except for I don't think $video_cost in the final price, but I'm no expert at reading this code. I tried this without success:

 $uploader_amount = $video_play_price - $charge;

Here is the full code, any help with line 50, will be appreciated.

<?php
if (IS_LOGGED == false) {
    $data = array('status' => 400, 'error' => 'Not logged in');
    echo json_encode($data);
    exit();
}

if (!empty($_POST['id'])) {

    if (!is_array($_POST['id'])) {
        $id_array[] = $_POST['id'];
    } else {
        $id_array = $_POST['id'];
    }

    // get cost video
    $db->where('name', 'video_play_price');
    $db_cost = $db->getOne('config');
    $video_cost = (float)$db_cost->value;

    $count_video = count($id_array);
    $user_id = $user->id;
    $wallet = (float)str_replace(',', '', $user->wallet);


	$amout = 0;
	foreach ($id_array as $id) {
            $video_id = (int)PT_Secure($id);

            // get video data
            $video = $db->where('id', $id)->getOne(T_VIDEOS);
			$amout += $video->video_play_price?$video->video_play_price:$video_cost;

	}

//   $amout = $video_cost * $count_video;

    $charge = ( $video_cost *0.50 );

    if ($wallet >= $amout) {

        $new_wallet = (string)($wallet - $amout);

        $db->startTransaction();

        $inserted_records = 0;
        foreach ($id_array as $id) {
            $video_id = (int)PT_Secure($id);

         $uploader_amount = $video_cost - $charge; 

            // get video data
            $video = $db->where('id', $id)->getOne(T_VIDEOS);


            // add data to paid table
            $insert_buy = $db->insert('u_paid_videos', [
                'id_user' => $user_id,
                'id_video' => $video_id,
                'session_key' => $_SESSION['session_key'],
                'video_play_price' => (string)$video_cost,
                'video_title' => $video->title,
                'user_id_uploaded' => $video->user_id,
                //'up_credit'=>$video_cost,
                'up_credit'=>$uploader_amount,
            ]);

            if ($insert_buy) { $inserted_records++; }
            //add wallet users' video
        $userwallet = $db->where('id', $video->user_id)->getOne(T_USERS);

        //$videouserwallet = $userwallet->wallet+$video_cost;
        $videouserwallet = $userwallet->wallet+$uploader_amount;
        $db->where('id', $video->user_id);
        $update_wallet = $db->update(T_USERS, [
          // 'wallet' => $videouserwallet,
            'wallet' => number_format($videouserwallet, 2, '.', ''),
        ]);
        }

        $db->where('id', $user_id);
        $update_wallet = $db->update(T_USERS, [
            'wallet' => $new_wallet,
        ]);


        if (($inserted_records == $count_video) && $update_wallet) {
            $db->commit();

            echo json_encode([
                'status' => 200
            ]);
            exit();
        } else {
            $db->rollback();

            echo json_encode([
                'status' => 400,
                'error' => 'Buy process error'
            ]);
            exit();
        }

    } else {

        echo json_encode([
            'status' => 400,
            'error_num' => 1,
            'error' => 'Not enough money'
        ]);
        exit();

    }

} else {

    echo json_encode([
        'status' => 400,
        'error' => 'Bad Request, Invalid or missing parameter'
    ]);
    exit();

}

I am trying to write a script for a puzzle based on the user's IP address, but I just can't wrap my head around how to do it. Essentially, when the visitor loads the page two things happen:

(1) a PHP application returns an image to serve as a background for the formula, 

(2) implement the algorithm of generating the formula based on IP, that is displayed on the image.

The puzzle itself would be in the form of ABC.DEF.GHI.JKL where each letter would be associated with the corresponding digit in their IP addy. The user is trying to solve for partial map coordinates. So, let's say the correct answer is N 35 54.374 W 084 01.829 and the user's IP is 075.036.025.058. The formula returned and placed on the image would be N 35 54. (E) (B) (F - H)  W 084 01. (L) (H) (B + H)

The algorithm basically needs to get the set of available digits from the IP and check if it can build the formula digits from those. If not, there would be a fallback for a missing number; for example given the above answer and if the available digits couldn't make a 9 then it would be represented by something like (C + 4).

Whatever I use as the final correct answer will not change and be the same for all users; only the puzzle formula would differ for each user as it would be based on their IP at the moment.

Any help here would be greatly appreciated. Thanks!

Gary