JSFiddle - React, Tailwind, and code Playground

HTML

<input id='amount-1' />
<input id='amount-2' />
<input id='balance' />

JavaScript

$('input[id*="amount"]').bind("keyup blur", function() {
    var balance = $('#balance').val()
       ,amount1 = $('#amount-1').val()
       ,amount2 = $('#amount-2').val()
       ,inputVal = $(this).val();

    if(amount1 - amount2 = balance){
        $('input[id*="amount"]').not(this).val(balance-inputVal);
    }
});