Answer:
C
Explanation:
There are 28 pencils inside the bag.
If there are 8 red pencils and the probability of choosing it is 2/7 then the total number of pencils inside the box is equals to 8 (the number of red pencil) ÷ 2 (the probability of choosing a red pencil) × 7 (the possibility space).

There 20 pencils that aren't red.
In getting the answer, just subtract the (number of red pencil) to the (total number of pencils in the bag.
28 - 8 = 20