Question 64675
First off, I'm assuming that Jeong is Janet's father.

Now Janet is 13 and Jeong is 31

Let's say that in x years from now Jeong will be twice as old as Janet

In x years from now, Janet will be 13+x years old
Jeong will be 31+x years old which has to be twice as old as Janet (2(13+x)) 

So our equation to solve is:

31+x=2(13+x) simplifying, we get:
31+x=26+2x collecting like terms, we will have:
31-26=2x-x or
x=5 years

ck
2(13+5)=31+5
2(18)=36
36=36

Hope this helps.  Happy holidays.-----ptaylor