JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <tr>
        <td>
            <input type="text" class="txtQuantity" />
        </td>
        <td>
            <input type="text" value="12,3" class="txtRate" />
        </td>
        <td>
            <input type="text" disabled="disabled" class="aspNetDisabled txtTotal" />
        </td>
    </tr>
</table>

JavaScript

$(document).ready(function () {
    $('.txtQuantity, .txtRate').change(function () {
        var txtQuantity = $('.txtQuantity').val();
        var txtRate = $('.txtRate').val();
        var total = parseFloat(txtQuantity) * parseFloat(txtRate);
        $('.txtTotal').val(total);
    });
});