JSFiddle - React, Tailwind, and code Playground

HTML

<form id="buy">
	<select name="years">
	    <option value="75">75</option>
        <option value="100">100</option>
        <option value="150">150</option>
       
	</select>
	<select name="names">
		<option value="70">70%</option>
        <option value="76">76%</option>
        <option value="81">81%</option>
       
	</select>

</form>
<input type="text" id="total" readonly="readonly" />

JavaScript

function setPrice () {
    var years = $('#buy').find('[name="years"]').val();
    var names = $('#buy').find('[name="names"]').val();
    var transfer = $('#buy').find('[name="transfer"]').val();
    var result = parseFloat(years / 100 * names).toString().split('.');
    if (result[1] === void 0) {
        result[1] = '';
    }
    while (result[1].length < 2) {
        result[1] += '0';
    }
    result = result[0] + '.' + result[1].substr(0,2);
    $('#total').val(result);
}
$('form>select').change(setPrice);
setPrice();