yashka,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<form name="sel">
<input type='radio' value='1' name="z">
<input type='radio' value='2' name="z">
<input type='radio' value='3' name="z">
<input type='radio' value='4' name="z">
<input type='radio' value='5' name="z">
<input type='radio' value='6' name="z">
<input type='radio' value='7' name="z">
<textarea id="text" name=""></textarea></form>
<script>
var s = document.forms.sel;
s.onchange = function(event) {
var l = s.querySelector('[name="z"]:checked');
document.getElementById('text').value = l.value||0;
}
</script>
</body>
</html>