JSFiddle - React, Tailwind, and code Playground

HTML

<input id="txt1" type="text" /><br />
<input id="txt2" type="text" /><br />
<input id="txt3" type="text" /><br />

JavaScript

$(function(){
    $(document).on('blur', '#txt1', function(){
        var one = $('#txt1').val();
        var two = $('#txt2').val();
        var three = $('#txt3').val();
        $('#txt3').val(one * two);        
    });     
    
        $(document).on('blur', '#txt2', function(){
        var one = $('#txt1').val();
        var two = $('#txt2').val();
        var three = $('#txt3').val();
        $('#txt3').val(one * two);        
    });       
    
});