The correct answer to this open question is the following.
The tone of this letter different from Khrushchev's letter on Day 9 in that "It is less emotional."
In this letter, Nikita Khrushchev, the Soviet Union leader, is answering that he agrees to United States President John F- Kennedy's terms.
In the letter, Nikita Khrushchev confirmed that there would be no attack or aggression of Cuba, not only by the United States but from any western nation. Then, the Soviet Union was going to act accordingly.
We are talking about one of the tensest moments during the Cold War years. The famous Cuban Missile Crisis of 1962.
During the Cuban Missile Crisis of 1962, President Kennedy had to be firm and cautious in making his decisions. The world was on the brink of a nuclear war. He decided to quarantine Cuba. The United States Navy ships blockade the ships coming to the island in order to certify that they had no nuclear weapons on them. The negotiations between the government of the United States and the Soviet Union were tense all the time until finally, both presidents reached an agreement.