<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html><head>
<script type="text/javascript">
function f() {
b = +document.getElementById('s1').value;
c = +document.getElementById('s2').value;
alert('b='+b);
alert('c='+c);
}
</script>
</head><body>
<select id="s1">
<option value="24500">24500
<option value="28700">28700
<option value="29900">29900
<option value="34300">34300
</select><select id="s2">
<option value="245001">245001
<option value="287002">287002
<option value="299003">299003
<option value="343004">343004
<option value="299005">299005
<option value="343006">343006
</select><br>
<input type="button" value="Вычислить" onclick="f()">
</body></html>