JSFiddle - React, Tailwind, and code Playground

HTML

<input type='text' id='input1'>
<input type='text' id='input2'>

CSS

#lc { background: #eeeeee; margin-bottom: 5px; width: 200px; border: 1px solid #bbbbbb; }
#edit { width: 200px; border: 1px solid #bbbbbb; }

JavaScript

$('input#input2').hide();

$('input#input1').keyup(function() {
    $('input#input2').show();
    var input1 = $('#input1').val();
    $('#input2').val( input1 - 2  );  // Use any equation here
    
    if( input1 == '' ) {
        $('input#input2').hide();
    }

});