Mine

<?
$a = 12;
$option[1] = 138;
$option[2] = 138;
$option[3] = 168;
if(isset($_REQUEST['Submit'])){
$overseas=$_REQUEST['overseas'];
$destination=$_REQUEST['destination'];

if ($destination == "USA and Canada"){
$k = 1;
} elseif($destination == "UK & Western Europe"){
$k = 2;
}else {
$k = 3;
}

echo ($overseas - $option[$k]) * $a;

}
?>