Boor while deleting emails in Gmail box separate here is easy step to delete all email in Gmail inbox quickly. Just follow this one.
img credit:- howtogeek

- Login to your gmail account and come into the inbox
- Click in the small box showing in the image.

- Now the screen change to this one

- Click on Select All in Primary (This option will appear once you check the box above)
- Click on Delete Button See in image below

You may also apply the same method in Social and Promotions,
Enjoy