JSFiddle - React, Tailwind, and code Playground

HTML

<select name="nm_field_3">
  <option value="Brown">Brown</option>
  <option value="Red">Red</option>
  <option value="White">White</option>
</select>

<select name="nm_field_4">
  <option value="80cm">80cm</option>
  <option value="100cm">100cm</option>
  <option value="120cm">120cm</option>
</select>

JavaScript

$(document).ready(function(){


    $('select[name=nm_field_3]').click(function(){
        var other_options = $('select[name=nm_field_4] option[value="120cm"]');
        var selected_option = $('select[name=nm_field_3] option:selected');
        if(selected_option.text() == 'Brown')
        {
            other_options.hide();
        }

        else
        {
            other_options.show();
        }
    });

});