As the letters explain each other, both are given here.

"I don't know exactly how, but the letter you read must have explained it."

Her office said a letter explaining the decision would be sent out this week.

Also, the letter explained why the matter should be kept confidential.

Hugh's last letter of 21 March 1549 explains his position.

The letter did not explain the remarks attributed to him earlier.

In that envelope is a letter explaining what I would like.

The letters sometimes explain the situations that the donors themselves are in.

After leaving her a letter explaining himself, he returns to his old school room to face the painting.

What if you receive a letter explaining that your friend is about to travel elsewhere.