Let the son be one year old before 12 years, and the father be 10a years old.

Now my son a+ 12 years old and my father 10a+ 12 years old.

12 years later, the son a+ 12+ 12 years old, and the father 10a+ 12 years old. That is, (a+24)x2= 10a+24, and a=3 is obtained.

So my father is 3x 10+ 12=42 years old now.