12. After completing her math homework, Lena prepared a problem for the math club session. She found two two-digit prime numbers that can be obtained from each other by swapping digits, and their difference is a perfect square. What numbers did Lena find?
12. The numbers found by Lena cannot contain even digits and the digit 5. They can only be written using the digits $1,3,7,9$. We have the numbers:
1) 31 and 13, but $31-13=18$ is not a square;
2) 71 and 17, but $71-17=54$ is not a square;
3) 97 and 79, but $97-79=18$ is not a square;
4) 73 and 37, and $73-37=36=6^{2}$.

Therefore, Lena found the numbers 73 and 37.