2. A natural number is written on the board. Every minute, the following operation is performed: if it contains two identical digits, one of them is erased; if all digits are different, the entire number is erased and replaced with a number three times larger. For example, from the number 57, you can get $57 \rightarrow 171 \rightarrow 71$ or $57 \rightarrow 171 \rightarrow 17$ in two minutes. Maria wrote a two-digit number and after several minutes, she obtained the same number again. Provide an example of how she could have done this.
Solution. $25 \rightarrow 75 \rightarrow 225 \rightarrow 25$ or $75 \rightarrow 225 \rightarrow 25 \rightarrow 75$.