Set to x years.

15+x=2(9+x)

15+x= 18+2x

2x-x= 15- 18

x=-3

That is, my brother was twice as old as my brother three years ago.

But this question asks my brother how many times before and after his age is twice that of my brother, which means it is a wrong question. Otherwise, something happened to my brother, and I still can't tell the time of the accident, Khan. If this problem is before the fourth grade of primary school, it can't be solved by setting an unknown number, so it can only be understood logically. 15-2*9=-3 means there is no solution.