The correct option is B 2018
Mathematically, both the comets will appear together after few years, which will be the common multiple of 9 and 6.
Multiples of 9 = 9, 18, 27, 36, 45...
Multiples of 6 = 6, 12, 18, 24, 30, 36...
So, after 2000, the comets will appear together after 18 years, 36 years, and so on.
The closest or next year from 2000 in which the comets will appear together is 2000 + 18 = 2018.