JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <tr>
        <td valign="top">
            <p>Contact Method:</p>
        </td>
        <td>&nbsp;</td>
        <td align="left" valign="top">
                <p>
                    <input style="width:20px!IMPORTANT;" type="checkbox" name="CheckboxGroup1[]" value="Phone" id="phone" />
                    <label style="margin-right: 25px;">Phone</label>
                </p>
                <p>
                    <input style="width:20px!IMPORTANT;" type="checkbox" name="CheckboxGroup1[]" value="Email" id="email" />
                    <label style="margin-right: 25px;">Email</label>
                </p>
                <p>
                    <input style="width:20px!IMPORTANT;" type="checkbox" name="CheckboxGroup1[]" value="Post" id="post" />
                    <label style="margin-right: 25px;">Post</label>
                </p>
        </td>
    </tr> 
    <tr id="hidden">    
        <td>
        <p>Address (if applicable):</p>
        </td>
        <td>&nbsp;</td>
        <td colspan="2"><input type="text" name="address" id="address" /></td>
    </tr>
</table>

JavaScript

$(document).ready(function() {    
    $("#post").change(function () {
        $("#hidden").toggle();
    });
})