JSFiddle - React, Tailwind, and code Playground

HTML

<table id="tabela">


    <tfoot>
        <tr>
            <td colspan="2"></td>
            <td align="right">Total: <span id="total" class="total"></span> </td>
        </tr>
    </tfoot>

    <tbody>
        <tr>
            <td>
                <input type="checkbox" value="16" class="price"> item A (16)</td>
            <td>
                <select value="" class="qty" name="qty">
                    <option value="1">1 unidade</option>
                    <option value="2">2 unidades</option>
                    <option value="3">3 unidades</option>
                    <option value="4">4 unidades</option>
                </select>
            </td>
            <td align="center"><span id="amount" class="amount">0</span></td>
        </tr>

        <tr>
            <td>
                <input type="checkbox" value="45" class="price"> item B (45)</td>
            <td>
                <select value="" class="qty" name="qty">
                    <option value="1">1 unidade</option>
                    <option value="2">2 unidades</option>
                    <option value="3">3 unidades</option>
                    <option value="4">4 unidades</option>
                </select>
            </td>
            <td align="center"><span id="amount" class="amount">0</span></td>
        </tr>

        <tr>
            <td>
                <input type="checkbox" value="61" class="price"> item C (61)</td>
            <td>
                <select value="" class="qty" name="qty">
                    <option value="1">1 unidade</option>
                    <option value="2">2 unidades</option>
                    <option value="3">3 unidades</option>
                    <option value="4">4 unidades</option>
                </select>
            </td>
            <td align="center"><span id="amount" class="amount">0</span></td>
        </tr>


    </tbody>
</table>

JavaScript

$(document).ready(function() {
    update_amounts();
    $('.qty, .price').change(update_amounts);
});


function update_amounts() {
    var sum = 0;
    $('table input:checked').each(function() {
		var tr = $(this).closest('tr');
        var qty = tr.find('.qty').val();
        var price = $(this).val();
        var amount = (qty * price) || 0;
        sum += amount;
        tr.find('.amount').text(amount);
    });

    $('.total').text(sum);
}