Question 1035703
Let x = number of years in the future.  

If Rony is 16 now, then his sister is 16/4 = years old now.

==> 16 + x = 2(4 + x)  ==> 16 + x = 8 + 2x  ==> x = 8.

Hence when Rony is 16 + 8 = 24 he will be twice as old as his sister.