JSFiddle - React, Tailwind, and code Playground

HTML

<select name="how" id="how" class="form-control c-select">
  <option value="0">Select Option</option>
  <option value="1">ICEF Brochure</option>
  <option value="2">ICEF Email</option>
  <option value="3">ICEF Sales Person</option>
  <option value="4">ICEF Print ad</option>
  <option value="5">Search Engine</option>
  <option value="6">External Website</option>
  <option value="7">Conference or Exhibition</option>
  <option value="8">Recommendation</option>
  <option value="9">Other</option>
</select>
<select name="SearchEngine" id="SearchEngine">
  <option value="0">Select Option</option>
  <option value="1">Google</option>
  <option value="2">MSN</option>
  <option value="3">Yahoo</option>
  <option value="4">Other</option>
</select>
<select name="SalesPerson" id="SalesPerson">
  <option value="0">Select Option</option>
  <option value="1">Harald Kreiner</option>
  <option value="2">Someone Else</option>
  <option value="3">Unkown</option>
</select>
<input type="text" id="how_details" name="how_details" />

JavaScript

$( document ).ready(function() {
  console.log( "ready!" );
  //hide on init
  var $SearchEngine = $("#SearchEngine");
  var $SalesPerson = $("#SalesPerson");
  var $how_details = $("#how_details");
  $SearchEngine.hide();
  $SalesPerson.hide();
  $how_details.hide();  
	$("#how").change(function (e) {
    var howValue = $(this).val();
    if (howValue == '1' || howValue == '2') {
      $how_details.hide();
      $how_details.val('');
    } else {
      $how_details.show();
    }
    if (howValue == '5') {
      $SearchEngine.show();
      $how_details.hide();
      $how_details.val('');
      if ($SearchEngine.val() == 4) {
        $how_details.val('');
        $how_details.show();
      }
    } else {
      $SearchEngine.hide();
    }
    if (howValue == '3') {
      $SalesPerson.show();
      $how_details.hide();
      $how_details.val('');
    } else {
      $SalesPerson.hide();
    }
    if (howValue == '0') {
    	$how_details.hide();
      $how_details.val('');
      $SearchEngine.val('0');
      $SalesPerson.val('0');
    }
	});  
  $SearchEngine.change(function (e) {
    var searchValue = $(this).val();
    if (searchValue == '4') {
      $how_details.show();
    } else {
      $how_details.hide();
      $how_details.val('');
    }
  });
});