Переключение активности у Input

$('#intro-class').change(function(){ 
   var val = $(this).val(); 
   if(val != 0) { 
     $('select').not($(this)).attr('disabled', true); 
     $('select').not($(this)).val(''); 
   } 
   else { 
     $('select').attr('disabled', false); 
   } 
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 
<div class="payment-wrap"> 
  <form class="calculator"> 
    <div class="container"> 
      <div class="row"> 
        <div class="wrap-calc"> 
          <label class="fst-lbl" for="intro-class">INTRODUCTORY CLASS</label> 
          <select id="intro-class" name="intro-class"> 
            <option value="0"></option> 
            <option value="intro-30">30 minutes</option> 
            <option value="intro-60">60 minutes</option> 
          </select> 
        </div> 
        <h3 class="payment__cup">LESSON PLANS 
        </h3> 
        <div class="wrap-calc"> 
          <label for="length">French course</label> 
          <select id="length" name="length"> 
            <option value="0"></option> 
            <option value="General">General Course</option> 
            <option value="Exams">Exams Preparation</option> 
            <option value="Conversational">Conversational French</option> 
            <option value="Business">Business French</option> 
            <option value="Civilisation">Civilisation française</option> 
          </select> 
        </div> 
        <div class="wrap-calc"> 
          <label for="students">For how many students</label> 
          <select id="students" name="students"> 
            <option value="0"></option> 
            <option value="indiv">Individual</option> 
            <option value="group">2-3 people</option> 
          </select> 
        </div> 
        <div class="wrap-calc"> 
          <label for="duration">Lesson duration</label> 
          <select id="duration" name="duration"> 
            <option value="0"></option> 
            <option value="lesDur-30">30 minutes</option> 
            <option value="lesDur-60">60 minutes</option> 
            <option value="lesDur-90">90 minutes</option> 
          </select> 
        </div> 
        <div class="wrap-calc"> 
          <label for="validity">Plan validity</label> 
          <select id="validity" name="validity"> 
            <option value="0"></option> 
            <option value="1month">One month</option> 
            <option value="3months">Three months</option> 
          </select> 
        </div> 
        <div class="wrap-calc"> 
          <div class="submit-block"> 
            <p>This French course costs : <span value="0" id="result-culc"></span> euros</p> 
          </div> 
        </div> 
      </div> 
    </div> 
  </form> 
</div>