<label for="note2" title="Passable">
    <a role="button" class="btn btn-note btn-xs" onclick="setVisibility('Note-question-sub', 'block');">
        <i class="fa fa-plus rouge" aria-hidden="true"></i>
        <span class="sr-only">Passable</span>
    </a>
    <input type="radio" value="2" name="note" id="note2" />
</label>

function setVisibility(id, visibility) {
    document.getElementById(id).style.display = visibility;
}