codice:
<head>
<script type="text/javascript">
function setValue(selectValue){
var newValue='';
switch(selectValue){
case '27': newValue=4075; break;
case '28': newValue=4175; break;
case '29': newValue=4275; break;
//ecc.
}
document.getElementById('targetInput').value=newValue;
}
</script>
</head>
<body>
<select onchange="setValue(this.value)">
<option value="27">27</option>
<option value="28">29</option>
<option value="28">29</option>
</select>
<input type="hidden" name="inputName" id="targetInput" />
</body>