Filch, means to steal something
Answer: Briony begins to see reality.
Explanation:
Briony wants to say she was introduced to real life. That the wrong "understanding" was an idea aimed at a deluded vision, nobody lives in a fairy tale and she had this "weak" idea because she was being awakened to reality through the observation of her own daily life and the people around her .
You know that the sum of a and b is 24, because the average is the sum of the numbers divided by the amount of numbers added together, and 12*2 is 24. Add 3 to 24 so you have 27, and then divide that by 3 because there are now 3 numbers in the set. The average of a, b, and c is 9.