Android Studio - Gradle Project Sync Failed

[Supratip]

Hello!
I can't start Android Studio properly. Every time gradle sync error occurs.
I've given a screen shot.
Any help would be appreciated.

 

[James_Watson]

I think your MainActivity should extend from class Activity, other than AppCompactActivity. Fix it and then try to sync.

 

[Supratip]

I think your MainActivity should extend from class Activity, other than AppCompactActivity. Fix it and then try to sync.

I've done that and everything related to gradle syncing but nothing's working now. A few days ago everything worked perfectly and then I updated the software. When I started it showed no error(gradle sync successful) and it showed an update available for gradle. When I updated it the error starts.
I've reinstalled android studio and the same case happens everytime.