Sum of Post and User field

<?php
$default_fees = get_field('acf_jobs_basefee');
$user_id = get_current_user_id();
$extra_fees = get_field('acf_jobs_extrafee', 'user_'.$user_id);
$extra_fees += $default_fees;
?>

<span>Fees: </span><?php echo $extra_fees; ?>%