JSFiddle - React, Tailwind, and code Playground

HTML

<div id="dprice1"><label><input id="price1" type="text" value="80" /></label></div>
<div id="dprice2"><label><input id="price2" type="text" value="100" /></label></div>
<div id="drate"><label><input id="rate" type="text"></label></div>

<input id="btnCal" type="button" value="Calculate">

JavaScript

$("#btnCal").click(function() {
    $("#rate").val(function() {
        var result = parseInt($("#price1").val()) * 100 / parseInt($("#price2").val());
        if (!isFinite(result)) result = 0;
        return result;
    });
});