The age difference between Xiaohong and Xiao Fang is 5 years. After 3 years, Xiaohong's age is from Xiao Fang. Four years ago, the age difference was 12 years.

According to the difference problem, Xiao Fang's age four years ago was 12/(3- 1)=6 years old.

So Xiao Fang's age is 6+4= 10, and Xiao Hong's age is 10+5= 15.