Using Include() to incorporate external PHP code

BEGIN PHP output

This is included text
But now I can add up... (4 + 4) = 8
<?php
print "This is included text<br />";
print "But now I can add up... (4 + 4) = ".(4 + 4);
?>

END PHP output

   <strong>
   <h2>
   <?php
     include("externalPHP.php");
    ?>
   </h2>
   </strong>
  

externalPHP.php