PHP Basics Learning Mode

What is the value displayed when the following is executed? Assume that the code was executed using the following URL:

testscript.php?c=25 
<?php
    function process($c, $d = 25)
    {
        global $e;
        $retval = $c + $d - $_GET['c'] - $e;
        return $retval;
    }
    $e = 10;
    echo process(5);
?>