Here is the result
$help_brother="30,45,12,13,14,15";
$force_world = '45,12,15';
$help_brother_array = explode(',', $help_brother);
$force_world_array = explode(',', $force_world);
$Result = array_diff($help_brother_array, $force_world_array);
echo implode(",",$Result);
You can get the following result.
If it helps then upvode the answer.