Miss Honey is stunned by Matilda’s ability to multiply high numbers.
Explanation:
Miss Honey seems to want to know if Matilda can multiply high numbers. She says "Are you sure?" as if she doubts Matilda's ability and then asks her to prove herself. Matilda does not seem as though she's trying to impress Miss Honey since she seems rather relaxed in the dialogue. She says, "I think so, yes" and "I'm fairly sure" which shows that she believes she can do it but isn't necessarily eager for this line of questioning.
