neeeeeddd helppppp php

[Minimeallolla]

it doesnt echo into the file

 if (isset($_POST['submit'])) { 

$firstname = ($_POST['firstname']);
$lastname = ($_POST['lastname']);

$filename = "***/$username.info.php" or exit("Unable to open file!");
$handle = @fopen($filename, 'x+')or die(mysql_error()); 
$content = ('$firstname');
@fwrite($handle, $content)or die(mysql_error()); 
@fclose($filename);
}

[trq]

Variables are not interpolated within single quotes.