JSFiddle - React, Tailwind, and code Playground

HTML

<table>     
<tr class="Violão">
    <td>Violão</td>
    <td class="td2 8">8</td>
</tr>
<tr class="Violão">
    <td>Violão</td>
    <td class="td2 23">23</td>
</tr class="Violão">
<tr class="Guitarra">
    <td>Guitarra</td>
    <td class="td2 16">16</td>
</tr>
</table>

JavaScript

var dictionary = [];

$("table tr").each(function() { 
    var thisName = $(this).attr("class");
    if ($.inArray(thisName, dictionary) == -1) {
        dictionary.push(thisName);
    }
});

for(var obj in dictionary) {
    var className = dictionary[obj];
    var total = 0;
    $("table tr." + className).each(function() { 
        total += parseInt($(this).children(".td2").text());
    });
    $("table tr." + className).append("<td>Total: " + total + "</td>");
}