JSFiddle - React, Tailwind, and code Playground

HTML

<div class="col-lg-4">
            <input class="custom_label_left form-control" type="text" name="start" id="start" placeholder="Van..." />
        </div>
        <div class="col-lg-4">
            <input class="custom_label_left form-control" type="text" name="end" id="end" placeholder="Naar..." />
        </div>
        <div class="col-lg-4">
            <button type="button" class="custom_label_left form-control btn btn-info" type="submit" onclick="dummyTest()">Bereken prijs</button>
        </div>
    </p>
    <p>
        <div class="col-md-12">
            <div class="col-sm-6">
                <h3>Ritprijs elders: €<span class="label label-danger" id="priceCalculated" ></span></h3>
            </div>
        </div>
    </p>
</div>

JavaScript

function dummyTest(){
var h =  parseFloat("5.3");
var m =  parseFloat("10.5");
var total = h+m;

document.getElementById("priceCalculated").textContent  = total.toString();

}