offset

hi, i’m not good with php so please bare with me. i got problem with my coding. i try to use a custom variable in a get_post function, but it’s not working.

example:

<?php $testa = 5 ;?>
<?php $testb = 10 ;?>

<?php $posts = get_posts(‘numberposts=$testa&offset=$testb‘); foreach ($posts as $post) : start_wp(); ?>

but only the $testa is called correctly in numberposts but not the $testb. how can i fix this?

please help
thank you