<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <H1 id="H1"></H1>
    <input type="button" id="Button1" onclick="displayValue()" value="Click Me">

    <script>
        function calculateSquare(Num1)
        {
            var result = Num1 * Num1;
            return result;
        }
        function displayValue()
        {
            document.getElementById("H1").innerHTML="The square is " + (calculateSquare(25) + 375);
        }
    </script>
</body>
</html>