JSFiddle - React, Tailwind, and code Playground

HTML

<table>                                                                       
      <tr class=='optional'>                                                                      
          <td>x11</td>                                                            
          <td>x12</td>                                                            
          <td>x13</td>                                                            
          <td class='required' rowspan='2'>x[12]4</td>                                                
      </tr>                                                                     
      <tr>                                                                      
          <td>x21</td>                                                            
          <td>x22</td>                                                            
          <td>x23</td>                                                            
      </tr>                                                                     
      <tr>                                                                      
          <td>x31</td>                                                            
          <td>x32</td>                                                            
          <td>x33</td>                                                            
          <td>x34</td>                                                            
      </tr>                                                                     
  </table>            
<br />
<input type='button' value='press me!'>

CSS

td {
    padding: 5px;
    border: 1px solid gray;
}

JavaScript

$('button').click(function(oe) {
   $('.optional').hide();
   $('.required').show();
});