3. Once in a train carriage, Tanya started to encrypt words by replacing letters with their numbers in the alphabet. When she encrypted the arrival and departure points of the train, she was surprised to find that they were written using only two digits: 211221 - 21221. Where is the train coming from and going to?
3. Let's write out all the letters of the alphabet:

| $\mathrm{A}$ | B | V | G | D | E | Yo | Zh | Z | I | Y | K | L | M | N | O |
| :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
|  |  |  |  |  |  |  |  |  | 0 | 1 | 2 | 3 | 4 | 5 | 6 |

![](https://cdn.mathpix.com/cropped/2024_05_21_e53d4ff4f2278a1c0d12g-053.jpg?height=63&width=1322&top_left_y=1533&top_left_x=367)
$\begin{array}{lllllllllllllllll}1 & 1 & 1 & 2 & 2 & 2 & 2 & 2 & 2 & 2 & 2 & 2 & 2 & 3 & 3 & 3 & 3\end{array}$ $\begin{array}{lllllllllllllllll}7 & 8 & 9 & 0 & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 0 & 1 & 2 & 3\end{array}$

The first word can start with either the second or the twenty-first letter of the alphabet (B or U). The second letter can then be either the first or the eleventh, or the first or the twelfth (A or Y, A or K).
BA or BY
UA or UK

Let's consider the first variant: BA.

The third letter can be either A (first) or K (twelfth), so we have the letter combinations BAA or BAK.

Then the fourth letter for the combination BAA can be either B (second) or F (twenty-second), so we get BAA B or BAA F. Completing the analysis of this variant, we have BAA BU, BAA FA, BAA BB. Clearly, the resulting letter combinations are not city names.

The fourth letter of the combination BAK can be either U (twenty-first) or B (second). In the first case, we have the word BAKU, in the second - no city name was formed. Thus, the city from which the train departs is BAKU.

The second word can start with either the letter B (second) or the letter U (twenty-first). Then the letter B can be followed by either A (first) or K (twelfth). In this case, we have the letter combinations BA or BK.

The letter U can be followed by either the letter F (twenty-second) or B (second). Then we have the letter combinations UF and UB. Clearly, by adding the last letter A (first) to the combination UF, we get the city UFA.

Thus, the train followed the route BAKU—UFA.

Answer: BAKU—UFA.