9 tasks are solved.Thanks.

app/Http/Controllers/CountryController.php

@@ -9,8 +9,7 @@ class CountryController extends Controller
     public function index()
     {
         // TASK: load the relationship average of team size
-        $countries = Country::all();
-
+        $countries = Country::withAvg('teams', 'size')->get();
         return view('countries.index', compact('countries'));
     }
 }

app/Http/Controllers/ProjectController.php

@@ -2,14 +2,22 @@
 
 namespace App\Http\Controllers;
 
+use App\Models\Project;
+use App\Models\User;
 use Illuminate\Http\Request;
+use Illuminate\Support\Facades\DB;
 
 class ProjectController extends Controller
 {
     public function store(Request $request)
     {
         // TASK: Add one sentence to save the project to the logged-in user
         //   by $request->project_id and with $request->start_date parameter
+        DB::table('project_user')->insert([
+            'project_id' => $request->project_id,
+            'start_date' => $request->start_date,
+            'user_id' => auth()->user()->id,
+        ]);
 
         return 'Success';
     }

app/Http/Controllers/UserController.php

@@ -3,12 +3,13 @@
 namespace App\Http\Controllers;
 
 use App\Models\User;
+use Illuminate\Database\Eloquent\Builder;
 
 class UserController extends Controller
 {
     public function index()
     {
-        $users = User::all();
+        $users = User::has('projects')->get();
 
         return view('users.index', compact('users'));
     }

app/Models/Attachment.php

@@ -4,15 +4,17 @@
 
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\MorphTo;
 
 class Attachment extends Model
 {
     use HasFactory;
 
     protected $fillable = ['filename', 'attachable_id', 'attachable_type'];
 
-    public function attachable()
+    public function attachable():MorphTo
     {
         // TASK: fill in the code to make it work
+        return $this->morphTo();
     }
 }

app/Models/Role.php

@@ -14,6 +14,6 @@ class Role extends Model
     public function users()
     {
         // TASK: fix this by adding a parameter
-        return $this->belongsToMany(User::class);
+        return $this->belongsToMany(User::class, 'users_roles');
     }
 }

app/Models/Team.php

@@ -14,7 +14,7 @@ class Team extends Model
     public function users()
     {
         // TASK: fix this by adding some extra code
-        return $this->belongsToMany(User::class);
+        return $this->hasMany(User::class);
     }
 
 }

app/Models/User.php

@@ -45,12 +45,12 @@ class User extends Authenticatable
     public function tasks()
     {
         // TASK: fix this by adding a parameter
-        return $this->hasMany(Task::class);
+        return $this->hasOne(Task::class, 'users_id', 'id');
     }
 
     public function comments()
     {
-        // TASK: add the code here for two-level relationship
+        return $this->tasks->hasMany(Comment::class);
     }
 
     public function projects()

resources/views/tasks/index.blade.php

@@ -1,5 +1,5 @@
 <ul>
     @foreach ($tasks as $task)
-        <li>{{ $task->name }} ({{ $task->user->name }})</li>
+        <li>{{ $task->name }} ({{ $task->user->name ?? '' }})</li>
     @endforeach
 </ul>