You can look at the postmark on the envelope. If it is a certified letter you may be able to track it.
Yes. Every letter mailed in the US needs a stamp.
The size of the letter and where it is being mailed from are important factors. If it is being mailed from California, the price would be very different from if it was being mailed from Japan.
3 days
Mailed ... it's the past tense of the action verb, mail as in to 'mail a letter.'
The direct object in the sentence is "letter." It is the recipient of the action performed by the subject "Leo."
If you mailed the letter, you may be able to use the tracking number associated with it, if you requested or received one. If you've just misplaced it, then clearing your head and taking the time to retrace your steps is the only way to go.
CERTIFIED
Tempe, Arizona
3 days
Postmark gives three things: date, time, and place mailed.
sent
1919.