This problem is from Chapter 21 of Manhattan 5lb book.
It says Sn =3n+3
Sequence S is defined for each integer n such that 0 < n < 10,000.

Quantity A is the median of sequence S, and
Quantity B is The mean of sequence S

I am not sure if the suggested answer C is the correct option. I plugged in 10 numbers starting with 6, and the median is greater than the mean actually

Hi, this is where the GM equal- not equal strategy comes into play. You could choose numbers 1,2,3,4,5- the result of which would be an evenly spaced set. In an evenly spaced set, the mean=median.
However, you could also choose random numbers 1,100 and 200 for n. In this case, mean will not equal median.
Hence, I believe D to be the correct answer.