<?php
$a = 2 + "2";
$b = 2 . "2";
echo "$a\n";
echo "$b\n";
echo 3 . $b - $b . "\n";
echo 3 . "12" - "1" . "\n";
echo 3 . "12" - "21" . "\n";
echo "312" - "321" . "\n";
?>

4
22
300
311
291
-9