How do I have my user input field calculate values based off data in my database?

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PHP

MySQL

I want to allow users to insert a number/quantity in the available input box that will then show/calculate a value/ answer based on data values from the database.

Eg: If they choose corn in the checkbox they will receive the nutritional value of that chosen food. They will then input their amount/quantity of that product and it will spit out it has x amount of fat, sodium, etc.

This is the output.php:

<pre><?PHP
require 'includes/dbh.inc.php';
include_once 'header.php';
require 'includes/output.inc.php';


?>

<div class="container-fluid">
    <div class="row justify-content-center">
        <div class="col-md-8">

            <?php

            if (isset($_SESSION['status'])) {
                echo "<h4>" . $_SESSION['status'] . "</h4>";
                unset($_SESSION['status']);
            }
            ?>
            <div class="card mt-5">
                <div class="card-header">
                    <h4>High Energy, Low Fiber Sources:</h4>
                </div>
                <div class="card-body">

                    <form action="includes/output.inc.php" method="POST">
                        <?php


                        $ingredient_query = "SELECT * FROM high_energy";
                        $query_run = mysqli_query($conn, $ingredient_query);

                        if (mysqli_num_rows($query_run) > 0) {
                            foreach ($query_run as $row) {
                        ?>
                                <input type="checkbox" name="ingredientlist[]" value="<?= $row['ingredients_name']; ?>" />
                                <?= $row['ingredients_name']; ?> <br />
                        <?php
                            }
                        }
                        ?>
                        <div class="form-group mt-3">
                            <button name="save_multicheckbox" class="btn btn-primary">Submit</button>
                        </div>
                    </form>

                </div>
            </div>
        </div>
    </div>
</div>

This is the includes for the output.php

<pre><?php
require  'dbh.inc.php';

// session

?>
<table class="table table-bordered table-sm">
    <thead class="">

        <tr>
            <td>Name</td>
            <td>Dry Matter</td>
            <td>Crude Protein</td>
            <td>Crude Fiber</td>
            <td>Ether Extract Fat</td>
            <td>Calcium</td>
            <td>Phosphorus</td>
            <td>Lysine</td>
            <td>Methionine</td>
            <td>Cystine</td>
            <td>Tryptophan</td>
            <td>MEn growing pig</td>
            <td>Energy digestibility, growing pig</td>
            <td>Nitrogen digestibility, growing pig</td>
        </tr>
    </thead>

    <?php

    if (isset($_POST['save_multicheckbox'])) {
        $ingredientlist = $_POST['ingredientlist'];

        foreach ($ingredientlist as $ingredientitem) {
            $query = "SELECT * FROM high_energy WHERE ingredients_name='$ingredientitem';";
            $query_run = mysqli_query($conn, $query);

            // $query_run = mysqli_query($conn, $query);

            if (mysqli_num_rows($query_run) > 0) {
                foreach ($query_run as $row) {
    ?>

                    <tbody>
                        <tr>
                            <!-- <td><?= $row['ingredients_id']; ?></td> -->
                            <td><?= $row['ingredients_name']; ?></td>
                            <td><?= $row['dry_matter']; ?></td>
                            <td><?= $row['crude_protein']; ?></td>
                            <td><?= $row['crude_fibre']; ?></td>
                            <td><?= $row['ether_extract_Fat']; ?></td>
                            <td><?= $row['calcium']; ?></td>
                            <td><?= $row['phosphorus']; ?></td>
                            <td><?= $row['lysine']; ?></td>
                            <td><?= $row['methionine']; ?></td>
                            <td><?= $row['cystine']; ?></td>
                            <td><?= $row['tryptophan']; ?></td>
                            <td><?= $row['MEn_growing_pig']; ?></td>
                            <td><?= $row['energy_digestibility_gp']; ?></td>
                            <td><?= $row['nitrogen_digestibility_gp']; ?></td>
                        </tr>
                    </tbody>
            <?php
                }
            }

            ?>

    <?php
        }
    }

What I have tried:

I have used switch statements but since I am new to PHP it is very hard to even find anyone who has done something like this.

<pre>$number = $_POST['number'];
    // $Number2 = $_POST['Number2'];
    $operator = $_POST['operator'];
    $Result = '';
    if (is_numeric($number) && is_numeric($query_run)) {
        switch ($operator) {
            case "Add":
                $ResultByT4Tutorials = $number + $query_run;
                break;
            case "Subtract":
                $ResultByT4Tutorials = $number - $query_run;
                break;
            case "Multiply":
                $ResultByT4Tutorials = $number * $query_run;
                break;
            case "Divide":
                $ResultByT4Tutorials = $number / $query_run;
        }
    }

I dont know what to do.