1.

<!DOCTYPE html>
<html>
<head>
	<title>Находим функцию.</title>
	<meta charset="utf-8">
	<script type="text/javascript">
		function average (x, y, z){
			return (x+y+z)/3;
		}
		let result = average (3, 4, 6);
		alert(result);
	</script>
</head>
<body>

</body>
</html>