Data Sufficiency

How do you solve this?

1. Average of first 9 integers is 7.
This implies 7 is the middle term in the series of 9 numbers.
We can write this series as :
3 4 5 6 7 8 9 10 11
Please note 7 is the middle term so that average could be 7.
Now as the series is of consecutive integers we can write the next 2 integers along this series as:
3 4 5 6 7 8 9 10 11 12 13
From which the average of 11 consecutive integers can be determined.

2. Similarly we can write a series with 9 as the middle term
5 6 7 8 9 10 11 12 13.
As these are the last 9 terms the other 2 terms can be written in the begining as
3 4 5 6 7 8 9 10 11 12 13
From which the average of 11 integers can be calculated.

Hence answer is D