Update amount of selected item(onChange)

Anybody can help me…I want to display the amaun_seunit when i click the drop down menu…

<select name=”no_rujukan_bil” id=”no_rujukan_bil” onChange=” biAmaunSeunit(this.value,this.form)”>
<option value=”0″>[Sila Pilih]</option>
</select>

<script language=”javascript” type=”text/javascript”>
function biAmaunSeunit(bill_refno,Frm) {
<?php
$Result4 = &$biModel->biListAmaunSeunit($Result3->field[‘bill_refno’]);
?>
var AmaunSeunit = new Array();

// set up the data to be consistent to start with.
document.Frm.no_rujukan_bil.selectedIndex=0;
document.Frm.amaun_seunit.value=AmaunSeunit[0];
var v = document.Frm.no_rujukan_bil.selectedIndex;
var x = document.Frm.no_rujukan_bil[v].value;
//var _y = eval(_x);
document.Frm.amaun_seunit.value = AmaunSeunit[$Result4->field[‘amaun_seunit’]];
}
</script>

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