$ is not defined

/*If this error occurs, include Jquery code in the HTML,
add jQuery code in footer i.e. just before the closing </body> tag. If you have not done that, then use the defer attribute. */
<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js" type="text/javascript"></script>