Did you get it right?
Two modern mailing details slipped into this 1950s post-office sorting room.

The Answer
The correct answer is: the padded plastic bubble mailer and its modern printed shipping label.
Here is why
- A padded plastic bubble mailer lies on the sorting table.
- The same mailer carries a modern computer-printed barcode shipping label.
Why people miss it
The two mistakes appear together and resemble ordinary mail until their materials and printing are inspected.
What answer did you get before checking?