JSFiddle - React, Tailwind, and code Playground

HTML

<table width="30%" border="0">
    <tr>
        <td width="30%" align="center" valign="center" bgcolor="#EEEEE0"> <font color="#8B8B83" face="arial"><b> - Estimativa de Carga T&eacute;rmica - </b></font>

        </td>
    </tr>
</table>
<br>
<table width="30%">
    <tr>
        <td width="30%">
            <form method="post" action "">
                <fieldset>
                    <legend></legend>
                    <table width="100%" border="0">
                        <tr>
                            <td width="50%" align="right" valign="center"> <b>Volume (&nbsp;m&sup3;): </b>

                            </td>
                            <td width="50%" align="center" valign="center">
                                <input type="text" name="volume" id="valor1" size="5" />
                            </td>
                        </tr>
                        <tr>
                            <td width="50%" align="right" valign="center"> <b>N&#186; de Pessoas: </b>

                            </td>
                            <td width="50%" align="center" valign="center">
                                <input type="text" name="pessoa" id="valor2" size="5" />
                            </td>
                        </tr>
                        <tr>
                            <td width="50%" align="center" valign="center">
                                <br>
                                <br>
                            </td>
                            <td width="50%" align="center" valign="center">
                                <input type="text" name="resultado" id="valor3" hidden/>
                                <input type="submit" value="Calcular Carga T&eacute;rmica" class="btn" />
                            </td>
                        </tr>
                    </table>
                </fieldset>
                <br>
                 <div class="resultado">
                     <h2>RELAT&Oacute;RIO</h2>

                    <div...

CSS

.resultado {
    font-weight: 600;
}
.resultado span {
    color: blue;
}

JavaScript

function somarValores() {
    var s1 = document.getElementById("valor1").value;
    var valor1 = convToFloat(s1) * 0.50;
    var s2 = document.getElementById("valor2").value;
    var valor2 = convToFloat(s2) * 12;
    return [valor1, valor2];
}

function convToFloat(temp) {
    if (temp.indexOf(',') == -1) temp = temp.replace(",", ".");
    return parseFloat(temp);
}

$(document).ready(function () {
    $(".btn").click(function (e) {
        e.preventDefault();
        var input = somarValores();
        $('#n1 span').text(input[0]);
        $('#n2 span').text(input[1]);
        $('#n3 span').text(input[0] + input[1]);
    });
})