This question has four answer choices:
2
4
6
8
The question do not have information enough to calculate a number.
But given the options given it is easy to answer. You just must know that
1) the pH scale is from 1 to 14
2) the pH of acidic compounds is below 7 (1 extremely acid and 7 is neutral).
3) the pH of basic compounds is above 7 (7 is neutral and 14 is extremely basic, or alkalyne).
So, the numbers 2, 4, and 6 are pH of acid solutions. Then only number, from the list, that corresponds to a pasic pH is 8.
Therefore, the answer is 8.