Примерно так
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<input id='term' class="input_style" name="term" type="text" value="" style="text-align: right;">
<input id='term2' class="input_style2" name="term2" type="text" value="" style="text-align: right;">
<script type="text/javascript">
term = document.getElementById('term');
term2 = document.getElementById('term2');
term.onkeyup = function(e){
term2.value = term.value * 8 / 3.4;
};
</script>
</body>
</html>
UPD: блин... опоздал на 20 минут...
