PHP Code not working on pages

Hi,
I’m trying to write some php code om a word press page. I have exec-php lugin activated but the editor basically strips the <?php tags and the php code is never processed

Any ideas as I’ve been struggling with this for 2 days now. I have other wordpress sites and they word perfectly

eg
<?php echo "hallo world<p>"; ?>

id stripped as:
`<!–?php <br ?–> echo “hallo world

“;