function getRadius(sentForm, make) {
   if(make=='Audi') {
      sentForm.rd.value = '50';
   } 
   else if(make == 'Dodge') {
      sentForm.rd.value = '20'
   }
   else {
      sentForm.rd.value='30';
   } 
}

function sendForm(sentForm, searchMake)
{
   var zip = sentForm.zc.value;
   
   if ((zip== '')||(zip.length<=4)){
	      alert("Please enter a valid ZIP code")
         return false;
   }
   if(searchMake == true) {
      var make = sentForm.mknm[sentForm.mknm.selectedIndex].value
      if(make == '') {
         alert("Please select a make");
         return false;
      }
      else{
         getRadius(sentForm, make); 
      }
   }
   sentForm.action='http://www.cars.com/go/search/search.jsp';
   sentForm.method='get';
   sentForm.submit();
   return true;
}