<?php

public function getTutorCourses(object $user): array
{
    return $this->getGroupsByUserId($user->id)
        ->transform(function (Group $group) {
            $this->setAdsToCourses($group->courses);

            return $group;
        });
}

protected function getGroupsByUserId(int $user_id)
{
    return Group::with('courses')
        ->where('tutor_id', $user_id)
        ->get()
}

protected function setAdsToCourses(Collection &$courses, int $num = 777)
{
    $courses->transform(function (Course $course) use ($num) {
        $course->ads = $num;

        return $course;
    });
}