SSC CHSL Model Paper 6

Manick's present age = 12
years, Rahul's present age = 4 years.
Let Manick be twice as old as Rahul after x years from now.
Then, 12 + x = 2 (4 + x)
12 + x = 8 + 2x
x = 4.
Hence, Manick's required age = 12 + 4 = 16 years.