JSFiddle - React, Tailwind, and code Playground

HTML

<input type='text' id='price' value='0.00'> x
<input type='text' id='count' value='0'> итого:
<span id="summ">0</span>

JavaScript

$('#price, #count').keyup(function(){
 parseFloat($("#summ").html(parseFloat($("#price").val())*parseInt($("#count").val())));
});