i wanted to get it so that when the html option with the id below is selected, the billing address fields show... this code isn't working, what am i doing wrong?

jQuery
$(document).ready(function(){
$("#billopt").focus(function(){
$("#billing").toggle();
});
});

<label>Subject:</label><br><select name="Subject">
<option>I have a general question</option>
<option id="billopt">I want monthly paid access</option>
<option>I have a suggestion.</option>
<option>I would like to book a skype tutoring session.</option>
</select><br>
<span id="billing" style="display:none;"><label><u>Billing Address:</u></label>
<br><input type="text" name="number">Street Address
<br><input type="text" name="aptnumber">Apartment # (if applicable)
<br><input type="text" name="city">City
<br><input type="text" name="state-province">State/Province
<br><input type="text" name="zip-post">Zip/Post code
<br><input type="text" name="country">Country
</span>