Admob/ Play services integraiton. Cannot resolve symbol error

i followed this tutorial to integrate admob in Android Studio. But now in the MainActivity AdFragment class a few symbols are red (**word* *) (Cannot resolve Symbol) and there is nothing in the error log.

   public static class AdFragment extends **Fragment** {

    @Override
    public **View** onCreateView(**LayoutInflater** inflater, **ViewGroup** container,
                             Bundle savedInstanceState) {
        return inflater.**inflate**(R.layout.fragment_ad, container, false);
    }

    @Override
    public void onActivityCreated(Bundle bundle) {
        super.**onActivityCreated**(bundle);
        AdView mAdView = (AdView) getView().**findViewById**(R.id.adView);
        AdRequest adRequest = new AdRequest.Builder().build();
        mAdView.loadAd(adRequest);
    }

}

Also in the activity_main.xml

<fragment android:name="com.appname.MainActivity$PlaceholderFragment"

PlaceholderFragment is red