The Two Digits in Jacks Age Are the Same As the Digits in Bills Age, but in Reverse Order.?

In five years Jack will be twice as old as Bill will be then. What is the difference in their current age.

Suggestion:

as of now, they are 13 and 31

in five years, they will be 18 and 36
{ 18 x 2 = 36 }

the difference between their current ages is 31 – 13 = 18