JSFiddle - React, Tailwind, and code Playground

HTML

<form method='POST' action='#'>
    <p>Помада</p>
    <span>Стоимость</span>
    <input type='text' value='300' name="sto" class="sto" disabled >
    <span>Кол-во</span>
    <input type='number' min="1" value="1" name="kolvo" class="kolvo">
    <p>цена</p>
    <input type="text" value="" name="cena" class="cena" disabled>
</form>
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<form method='POST' action='#'>
    <p>Духи</p>
    <span>Стоимость</span>
    <input type='text' value='500' name="sto" class="sto" disabled >
    <span>Кол-во</span>
    <input type='number' min="1" value="1" name="kolvo" class="kolvo">
    <p>цена</p>
    <input type="text" value="" name="cena" class="cena" disabled>
</form>

JavaScript

jQuery(document).ready(function(){
var sto = $(".sto").val(), kolvo = $(".kolvo").val();
$(".cena").val(sto*kolvo);
$(".sto, .kolvo").on('input', function() {
sto = $(".sto").val();
kolvo = $(".kolvo").val();
$(".cena").val(sto*kolvo);
});
});