JSFiddle - React, Tailwind, and code Playground

by aka_SKIff

HTML

<input type="radio" class="b-form-input" name="event" value="b-form-input-contract" id="b-form-input-contract1">
<label for="b-form-input-contract1">Указать другое событие</label>
<input type="text" style="margin-left: 210px; vertical-align: super;" name="contractAgree" disabled>

JavaScript

$('#b-form-input-contract1').on('change', function() {
  if ($('#b-form-input-contract1').is(':checked'))
    $('input[name="contractAgree"]').prop('disabled', false);
  else
    $('input[name="contractAgree"]').prop('disabled', true);
});