How many intervals will there be between mail pickups? Recall problem 4.

## Solution

If the mail is picked up 5 times within the specified time, there will be 4 intervals, i.e., the duration of one interval will be 3 hours.

## Answer

Every 3 hours.
[ Arithmetic. Mental calculation, etc.]

On the mailbox, it is written: "Mail is collected five times a day from 7 to 19 hours." Indeed, the first time the postman collects the mail is at 7 in the morning, and the last time is at 7 in the evening. At what intervals are the letters taken out of the box?