JSFiddle - React, Tailwind, and code Playground

HTML

<html>
    <body>
        <input type="text" id="emailDown">
        <input type="text" id="internetDown">
        <input type="text" id="serverDown">
        <input type="text" id="pcDown">
        
        <div id="totalHoursDown"></div>

JavaScript

$(function(){
    var $fields = $('#emailDown, #internetDown, #serverDown, #pcDown'),
    $totalHoursDown = $('#totalHoursDown');
    $fields.change(function() {
        var sum = 0;
        $fields.each(function() 
                 { 
                     var val = parseInt($(this).val(), 10);
                     sum += (isNaN(val)) ? 0 : val; 
                 });
        $totalHoursDown.html(sum);
    });
});