Form redirect after submit based on two specific form options using javascript/html

This is my attempt, which currently doesn't work. I want someone to be able to pick a location and a type of event. This will then determine what web page they get redirected to. Im not too sure what I am doing wrong.

<form name="signupForm" id="signupForm" target="_top" method="post" action="http://ift.tt/1Rkuojp" onsubmit="get_action(this);">

<table><tbody>
<tr>
<td> 
<ul id="teamFields"> 

  <li class="formRow emailRow" id="field_Email"><label class="fieldName" for="signup_Email">Email<span class="reqMarker">*</span></label>
<input type="text" name="Email" maxlength="64" value="" id="signup_Email" class="inputTextField" />
<div id="emailEntryAlert">
</div>
</li> 


<li class="formRow userFieldName" id="field_User5" ><label class="fieldName" id="labelUser5" for="signup_User5">Please select the closest city to where you live from the list<span class="reqMarker">*</span></label> <select name="User5" id="signup_User5"><option value="">Choose</option> <option value="London" >London</option><option value="Birmingham" >Birmingham</option><option value="Manchester" >Manchester</option></select>
</li> 

</li> 
<li class="formRow userFieldName" id="field_User8" ><label class="fieldName" id="labelUser8" for="signup_User8">Would you like to attend the workshop and/or audition?<span class="reqMarker">*</span></label> <select name="User8" id="signup_User8"><option value="">Choose</option> <option value="Workshop Only" >Workshop Only</option><option value="Workshop + Audition" >Workshop + Audition</option><option value="Audition Only" >Audition Only</option></select>
</li> 


</ul>
<ul id="teamSelection"> 
<li class="formRow joinRow"><span id="confirmText"> </span>
</li> 
<input type="hidden" name="AutomaticTeamIDs" value="4" /> 
<input type="hidden" name="AutomaticTeamIDs" value="3" /> 
<input type="hidden" name="AutomaticTeamIDs" value="1" /> 
</ul> 
</td> 
</tr> </tbody>
</table> 
<div id="reqInfo">* required information
</div> 
<input id="formSubmit" type="submit" name="formSubmit" style="font-weight: bold; font-size: 16px; color: #000000; border-style: solid; border-width: 8px !important; border-color: #d3d3d3 !important; border-radius: 0px !important; padding: 16px !important; background: #a9a9a9 !important; box-shadow: none !important;" value="Sign Me Up" /> 
<input type="hidden" name="Referrer" value="" /> 
<input type="hidden" name="qstring" value="9ec6ce8b4e17b30b7c2a75edc1c1a684716721de718b4187c3ac601cb070094b" /> 
<input type="hidden" name="formSubmitCheck" value="1" /> 


<script type="text/javascript">
    function get_action(form) {
        var optn = document.getElementById("signup_User5");
        var optn_value= e.options[e.selectedIndex].value;
        var option = document.getElementById("signup_User8");
        var option_value= e.options[e.selectedIndex].value;

        if ((option_value=="Workshop Only") && (optn_value=="London")) {
           window.location.href = "http://ift.tt/1EnTe80";
     } else if ((option_value=="Workshop Only") && (optn_value=="Birmingham")) {
           window.location.href = "http://ift.tt/1RkuozD";
     } else if ((option_value=="Workshop Only") && (optn_value=="Manchester")) {
           window.location.href = "http://ift.tt/1EnTe84";
    } else if ((option_value=="Audition Only") && (optn_value=="London")) {
           window.location.href = "http://ift.tt/1RkuozF";
    } else if ((option_value=="Audition Only") && (optn_value=="Birmingham")) {
           window.location.href = "http://ift.tt/1EnTeok";
    } else if ((option_value=="Audition Only") && (optn_value=="Manchester")) {
           window.location.href = "http://ift.tt/1RkuqHR"; 
    } else if ((option_value=="Audition + Workshop") && (optn_value=="London")) {
           window.location.href = "http://ift.tt/1RkuozF";
    } else if ((option_value=="Audition + Workshop") && (optn_value=="Birmingham")) {
           window.location.href = "http://ift.tt/1EnTeok";
    } else if ((option_value=="AAudition + Workshop") && (optn_value=="Manchester"))
           window.location.href ="http://ift.tt/1RkuqHR"; 

}
    }

</script>

</form> 
<div id="formBottom">
</div> 
</div> 
</div> 
</body>
</html>